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Archive-name: arch-storage/part1
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See reader questions & answers on this topic! - Help others by sharing your knowledge
Rod Van Meter, Joe Stith, and the gang on<BR> or

Information on disk, tape, MO, RAID and SSD can be found in part 1 of
the FAQ.  Part 2 covers file systems, hierarchical storage management,
backup software, robotics, benchmarking, MTBF and miscellaneous

$Header: /nfs/yelo/rdv/comp-arch-storage/faq/RCS/FAQ-1.draft,v 1.38 98/01/16 18:19:48 rdv Exp $

        Many items merely identified, not described.

        Last updated: 1997/9/18

        Most recent changes:

		THIC (Tape Head Interface Committee)
		HD Forum @ Blue Planet
                Storage system issues, both software and hardware

1.     Editor's Note

2.     Disclaimer

3.     Original Editor's notes

4.     Truly Frequently Asked Questions

5.     Tape
5.1.   Cartridge vs Cassette
5.2.   Longitudinal
5.3.   Serpentine
5.4.   Helical Scan
5.5.   Tape Media Lifetimes (Longevity) {Brief}
5.6.   9-track {brief}
5.7.   3480/3490/3490E {brief}
5.7.1. New IBM Tape (NTP) 3590
5.8.   Magstar Coyote (IBM 3570) {Brief, New}
5.9.   QIC {brief}
5.9.1. Travan TapeStor {brief,new}
5.10.  4mm {brief}
5.11.  8mm {brief}
5.11.1. Mammoth (EXB-8900) {Brief}
5.11.2. Sony SDV-300 {New}
5.12.  DLT {full}
5.12.1. DLT7000 {Brief}
5.12.2. DLT4000
5.12.3. DLT2700 (from DEC)
5.12.4. DLT2000 (from DEC (now Quantum))
5.13.  MountainGate (was Metrum) VHS {brief}
5.14.  VCR VHS
5.15.  19MM (D1 and D2) {Brief}
5.16.  ID-1
5.16.1. DATATAPE
5.16.2. Sony
5.17.  D-2
5.18.  StorageTek Helical {Brief}
5.19.  Optical
5.20.  D-6 {brief}
5.21.  D-3 {brief}
5.22.  Sony DTF {Brief}
5.22.1. GY-2120 {New}
5.23.  DATATAPE DTR-48 {Brief}

6.     Disk
6.1.   CAV, ZCAV and CLV
6.2.   Optical {Brief}
6.2.1. CD-ROM DVD (Digital Versatile Disk) (Next-Generation CD) {New} GIANT CD-ROMS {New}
6.2.2. WORM {brief} Sony {brief}
6.2.3. Erasable Magneto-Optical Physics Sony MiniDisc {Brief,New} Magneto-optical, 5.25-inch Magneto-optical ZCAV, 5.25-inch HP Corsair {Brief} Maxoptix T4-1300 Pinnacle Micro {New} Asaca HSMO {Brief} Other Multi-beam MO {None} 3.5-inch MO {Brief} Sony {Brief} Nikon 12-inch MO {Brief} Sony 12-inch MO {Brief} NEC 12-inch MO {Brief}
6.2.4. Electron-Trapping {None}
6.2.5. Dual Function {Brief} Panasonic/Toray {Brief} IBM {None}
6.3.   Magnetic
6.3.1. 5.25-inch Seagate
6.3.2. 3.5-inch IBM
6.3.3. Hard Disk Manufacturers {Brief}
6.3.4. Bernouli {None}
6.3.5. Floptical {Brief}
6.3.6. PC Removables {Brief} SyQuest EZ135 {Brief} Iomega Zip {Brief} Iomega Jaz {Brief} SyQuest Removable Cartridge hard Drives Kalok removable cartridge hard drives
6.3.7. Mainframe {Brief}
6.4.   Other

7.     RAID {Full}
7.1.   RAID Levels
7.2.   RAID-6
7.3.   John O'Brien and RAID-7
7.4.   RAID Papers
7.5.   R-Squared {Brief}
7.6.   Sun {Brief}
7.7.   Clariion {Brief}
7.8.   BayDel {Brief, New}
7.9.   the RAIDbook {Brief}
7.10.  Software Striping {Brief}
7.11.  RAID Vendors

8.     Solid State Disk (SSD) Frequently Asked Questions (FAQ)

9.     Other Devices
9.1.   Holographic Storage Products {Brief,New}
9.2.   TeraStor {Brief, New}

10.    RAIT (Redundant Arrays of Inexpensive Tape)
10.1.  DataVast (was VastNSS)

11.    RAOT (Redundant Arrays of Other Things :-)

Subject: [1] Editor's Note From: Editor's Note I took over the maintenance of the C.A.S FAQ from its originator, Joe Stith (, Fermi National Accelerator Laboratory, at the time), in July '94. I have made many additions and edits of my own. It should be available on the various FAQ servers. Apologies for the under-construction formatting and lack of better referencing. I will add as my expertise and time allows and will include submissions sent to me (Rod Van Meter, and information put into the newsgroup by others. Yes, some of the submittals are from vendors (including me, see the disclaimer). If you post to the newsgroup and find yourself quoted in this FAQ but wish to be removed, please let me know. There is more information in my (still primitive) WWW version of the FAQ, including more commercial info. It is temporarily available at, but this is probably not a good permanent home for it (volunteers?). I have also started working on a Japanese translation available there (only about 10% complete). There is also a good group of FAQs (including this one) stored at; prettier and easier to use but with only the info I actually post. The size of these FAQs is getting out of hand; I'm open to suggestions on material that doesn't really belong in a FAQ or areas where I'm simply too verbose (I may reduce the DLT info since there is now a separate FAQ). SHMO: when you see this, it means "Somebody Help Me Out!" I'm actively soliciting information on this topic. See the copyright notice near the end.
Subject: [2] Disclaimer From: Disclaimer I used to work for ASACA, which makes Metrum's (now Mountain Gate) robotics and makes a 12 MB/sec. magneto-optical disk drive, and resells AMASS in Japan. I now work at USC's Information Sciences Institute working on the Netstation project (essentially, network-attached peripherals and high-speed networking). This information is included so you can identify my bias. Obviously the things that I know the most about are the best-represented. I attempt to be as impartial as possible; if you have complaints about my fairness, let me know. None of this should in any way be construed as the official opinions of ASACA, USC/ISI or Caltech, and may not even represent MY opinions.
Subject: [3] Original Editor's notes From: Original Editor's notes I believe a reference would be useful and I am willing to pull it together... I have included the original call for votes and will go through that list for other ideas to include. I will also format this for sending to news.answers, misc.answers, and comp.answers. As I am writing this, "{None}" indicates I have not written anything for it yet, {Full} indicates it is OK, while {Brief} indicates somewhere in the middle. {New} indicates some new information has been provided. (joe stith, early '94) =========DISCLAIMER===== This information is believed to be reasonably accurate although I do not verify every submission. No legal liability is assumed. See full disclaimer at end.
Subject: [4] Truly Frequently Asked Questions From: Truly Frequently Asked Questions Also see the miscellaneous section near the end of part 2 of the FAQ. * How do I connect X to Y? Try asking in the appropriate comp.periphs.x or comp.sys.y groups. * What about the jumper settings for my Yoyodyne 4000? Try asking in the appropriate comp.periphs.yoyodyne group. This group attempts to keep the discussion at a higher level. * Can somebody recommend a PC or Unix backup package? (SHMO) The Aug. '94 issue of PC World has an article covering PC tape drives (mostly QIC), and covers backup software to some extent as well. Try asking this question in the PC-related newsgroups. I've started adding a list of backup software to part 2 of this FAQ, though it's not very complete yet. * What about DAT/DLT/8mm/...? Covered in the sections on tape drives & media. There is also a DLT-specific FAQ maintained by a guy from DEC posted occassionally here. * Does anybody have the phone number of...? There's a long list currently posted to: (inside FAQ) and in biz.zeos.general. For the WWW-enabled, check out * What about RAID7? See the description under RAID arrays; NOT a popular topic around here. * MTBF? This topic is responsible for generating the most heat in this group. There are a few sentences about it in part 2 of the FAQ, but I'm not qualified to write this section (and/or not willing to suffer the public humiliation :-).
Subject: [5] Tape From: Tape (No compression added in calculations unless specified otherwise)
Subject: [5.1] Cartridge vs Cassette From: Tape Cartridge has only one reel (i.e. 3480, DLT). Cassettes have two reels (i.e., 8mm, 4mm, 19mm, VHS) and may not need to be rewound to dismount.
Subject: [5.2] Longitudinal From: Tape have heads that write bit streams that are parallel to the edge of the tape.
Subject: [5.3] Serpentine From: Tape are longitudinal that write the full length of the tape, then turn around and write the length of the tape in the opposite direction with the heads in a slightly different position. This process may repeat many times.
Subject: [5.4] Helical Scan From: Tape are like your VCR with a rotating head mounted at an angle writing "swipes" at an angle not parallel to the edge of the tape. The tape is moved only slightly between swipes. Two or so longitudinal tracks may also be used for fast positioning purposes.
Subject: [5.5] Tape Media Lifetimes (Longevity) {Brief} From: Tape See and for some info on this topic. Other contributions gladly accepted, this topic comes up frequently in the newsgroup. (rdv, 1996/3/20)
Subject: [5.6] 9-track {brief} From: Tape The old 2400 foot round reel of tape written at 800, 1600, or 6250 BPI.
Subject: [5.7] 3480/3490/3490E {brief} From: Tape Square cartridge: serpentine IBM 3480 - 18 track - 200 MB/cartridge, 1984 IBM 3490 - Smaller packaging, IDRC standard, 1989 reports that it is a 3480 in ID string IBM 3490E - 36 track, double length - 800 MB/cartridge native, 1992 IDRC data compression is also available. These drives have traditionally come from the mainframe vendors -- IBM, Fujitsu, Storage Tek, etc. They were originally very large objects, with vacuum columns and mainframe interfaces, the size of large filing cabinets. However, recently they have become available in smaller packages, 19" rack mount or table top, and with interfaces such as SCSI. Here's one from last year that I recently dug out of some old mail: IBM has just made generally available the following: 3490E Model E SCSI tape drive fast/wide differential IDRC compression 3 MB/sec at the tape head, 6.5 MB/sec with compression approx 800 MB tape capacity with out compression, 2.4 GB with a 3:1 comp 7 tape CSL(cartridge stack loader) Desk top and rack mount List $27,000, 94/4/11 There's also a standalone drive with a small autoloader from a company called Overland Data. Their L490e is a win because it reads and writes both 18 and 36 track tapes. At $20K it's reasonably priced. For the www-enabled, see (, 94/12/21)
Subject: [5.7.1] New IBM Tape (NTP) 3590 From: Tape Same form factor as 3480, serpentine. 9 MB/sec., 10GB/cart. Bare drive should retail ~$35K, 1Q95. Two SCSI interfaces? Robotics also planned. (, 09/30/94) NTP has been released (95/4/10) as the 3590 tape subsystem with the Magstar tape drive. The press release didn't mention price, availability, or interfaces (though it did say attachable to Suns, RS-6k, etc.). list price for the 3590 drive is approximately $43.5K; list for media is approximately $50; list for 3590 drive + 10 cartridge stacker is approx $48K (95/9/18, IBM Storage has an excellent WWW page at
Subject: [5.8] Magstar Coyote (IBM 3570) {Brief, New} From: Tape There is a second type of tape drive from IBM based on the Magstar technology. Known as Coyote or 3570, it's 2.2 MB/sec., 5GB in a two-reel cassette. Unlike 3590, the tape never leaves the cassette. The width of the tape is much less than 1/2", maybe 1/4"? The cassette is about the size of an 8mm, give or take. There's an associated desktop modular autochanger. (rdv, 97/6/5)
Subject: [5.9] QIC {brief} From: Tape Quarter Inch Cartridge. Primarily low-end (ie, PC) available from multiple vendors but 3M is pushing it into midrange market with estimates of 100 Gigabytes per cartridge by 1999. Two-reel cassette. In Dec '94, 3M, Sony, HP and others announced a new format, 2.3 times the capacity, available mid-1995. The cartridge and drive mechanics apparently change. It will be .315 inch tape instead of .25, with 750 feet of media in a cartridge. (rdv, 94/12/16)
Subject: [5.9.1] Travan From: Tape Travan is a 3M trademarked name for a new family of data minicartridge tape media. Travan provides additional capacity via longer length(750' / 229 meters) and greater width(.315" / 8mm) tape then previous generations of data minicartridge. Drives that can accommodate Travan cartridges must have a mechanism that can handle wider tape (.315" / 8mm vs. earlier data minicartridge that are .25"/6.2mm) and be able to accept the slightly larger Travan cartridge. All major drive manufactures have modified existing drives or designed new mechanisms to accommodate the Travan cartridge. Today's Travan capable minicartridge tape drive maintains the industry standard QIC formats. These drives can write and read smaller capacity data minicartridge tapes of the same QIC format family(See below). Travan TR1 capable drive functionality Cartridge Format Capability Native Capacity DC2120 QIC-80 W/R 120MB DC2120XL QIC-80 W/R 170MB QW5122F QIC-80 W/R 208MB TR1(Travan) QIC-80 W/R 400MB Travan TR3 capable drive functionality Cartridge Format Capability Native Capacity DC3010XL QIC3010 W/R 346MB QW3010XLF QIC3010 W/R 425MB DC3020XL QIC3020 W/R 692MB QW3020XLF QIC3020 W/R 850MB TR3(Travan) QIC3020 W/R 1600MB Note 1. TR3 capable drives can read only all combinations of QIC-80 formatted tapes 2. 3M has developed a TR2 800MB QIC3010 format tape but has not gone to market with it at this time 3. There will be TR4 and greater media products in the future. These products will offer greater capacity and performance. (thanks to, aug 16 1995)
Subject: [] TapeStor {brief,new} From: Tape The TapeStor 800 and 3200 from Seagate are Travan TR1 and TR3 drives, respectively, targetted at the home PC market. (rdv, 96/11/4)
Subject: [5.10] 4mm {brief} From: Tape Multiple vendors. Initially for home audio market. Original product held 1.3 GB on one 60 meter tape at about 180 KB/second. Search speeds run about 200 times nominal speed. DDS (Digital Data Storage) format has overtaken the DATA/DAT format. Two-reel cassette. gives HP DDS drive information gives specs for the DDS2 C1533A
Subject: [5.11] 8mm {brief} From: Tape Sony developed transport designed initially for home video market. Exabyte has U.S. rights with Kubota qualifying as a second source when needed. EXB 8200 model holds 2.3 Gigabytes per tape at 220 KB/sec EXB 8500 model holds 5 Gigabytes per tape at 500 KB/sec Search speeds of the 8200 is dismal, but is significantly improved in later models. Compression and half-height (standard is full-height 5.25-inch) features are also available. See for more info.
Subject: [5.11.1] Mammoth (EXB-8900) {Brief} From: Tape Mammoth is the new Exabyte drive. It holds 20 GB uncompressed per cartridge, with a transfer rate of 3 MB/s. Exabyte has been touting this drive since at least April '93; it is now shipping. SCSI-2 fast or fast & wide interface. Read (not write) compatible with all older Exabyte drives. (rdv,96/11/1)
Subject: [5.11.2] Sony SDV-300 {New} From: Tape An article in Computer Tech Review says that Sony has announced a 25GB native 3MB/sec 3.5" 8mm drive based on the same media technology they developed for Exabyte's mammoth. At this point (June 10, 1996), opinions in the newsgroup differ as to whether or not the _media_ is compatible with Exabyte's Mammoth, though everybody agrees that SDV-300 will not be read or write compatible with Mammoth or earlier Exabytes. Sony's new drive does look impressive. The information that I have says that production shipments begin this summer (late July for initial shipments) for units without the data compression feature. That would be 25GB native capacity @ 3MB/sec. Drives with compression will ship in 4Q96, for a guess, probably October-ish. The interesting feature is the NIC cartridge that has positioning information due out by mid-97 that will eliminate the need to rewind before unloading the tape and will allow the tape to seek in either direction on loading. This is a flash chip built into the cartridge itself. The SDX-300C is apparently one model in this line, already shipping in some autochangers. No flash index chip yet. (rdv,96/11/4) (Jeff Johnson (, Bob Covey ( and others, 1996/6/10)
Subject: [5.12] DLT {full} From: Tape See for info on current issues concerning DLT. Also see the DLT FAQ, maintained by Larry Kaplan, For Suns, there is info at Digital Linear Tape (DLT) TZ87 (DLT2000) - 10 GB native per cartridge See also robotics (DLT2700 is 7 tape library) Ref: Digital's Customer Update, March 14, 1994 Serpentine recording. Developed from DEC's TK50 & TK70 technology. The unit that developed this was sold to Quantum. DLT is the new tape technology getting the most air time around here. There is also a DLT-specific FAQ maintained by Larry Kaplan from Quantum. See for specifications, for some FAQ answers. I also have an old copy of Larry Kaplan's different FAQ available at From the newsgroup: Tape uses a special hook for load/unload mechanism. DEC is the initial vendor, but other vendors are re-selling them (sort of like TTI's reselling of the Exabyte 8mm tape drive). Transfer rate of 2.5 MB/sec, but that assumes 2:1 compression, so it is 1.25 MB/Sec native. Likewise the 20 GB cartridge is 10 GB native. DLT4000 ($2K upgrade from DLT2000) soon (9/94?) Double the capacity. Some agreement with Cypher. Still not shipping in quantity, 1/95. Can be used on NON-DEC systems (standard SCSI interface). One report of a batch of tapes that were "too wide". > (Michele Michelotto) wrote: >You're comparing the top QIC format with the rather new DLT tecnology. What is so special about DLT? I'll try to answer: >1. Serpentine format means that there are several parallel tracks. the head goes down the first track and comes back down the second one etc. If I need to access a file at the end of the "logical tape" and the drive knows that it is at the beginning of the 52th track it goes directly to the 52th track and start seeking on it. So the worst case access time is close to the rewind time (about 100 sec) the average access time is about (60 sec). >2. the unit I tested was a 6 GB/cartridge (no compression) 700 kB/sec. the cartridge had 112 tracks but since the drives use two heads, it could access track N and track N+54 together. So it looked like a 54 track cartridge. Now it's very easy to put 4 (or 8) heads in the drive and double (or multiply by 4) the transfer speed while maintaing the backward compatibility (with 8 head you use only head #1 and #5 to emulate a 2 heads unit). >3. DEC is selling to the OEM a DLT4000 unit with 20GB uncompressed (40GB with compression). [may be available 9/94]. [Thinner, longer tape plus somewhat higher density and slightly more efficient packing/blocking] DLT cost $5K US for 20GB drive, $10K for a 140GB stacker, $150K for a 3.2 TB robot. Autochangers are made by DEC, Odetics (available through EMASS) and Metrum (now MountainGate). Piping tar into dd, with a bs=64k can increase your speed. The drives have a tape mark directory that is used for a SPACE command, but if you just SPACE 1 FILEMARK multiple times, efficiency is poor (and is the fault of the software implementation as it should "SPACE n FILEMARKS"). Submitted (approved?) ANSI standard, but that does not mean anyone other that DEC is doing anything more than OEM'ing it.
Subject: [5.12.1] DLT7000 {Brief} From: Tape 35 GB on a cartridge (uncompressed), 5 MB/sec. transfer rate. Drives available in limited quantities now, general availability was targetted for June/July '96, but still apparently months away? (Alex Brill,, 1996/2/23, updated rdv, 96/7/8)
Subject: [5.12.2] DLT4000 From: Tape Streaming tape drive Quoted 40 GB includes 2:1 compression Quoted 3.0 MB/sec includes 2:1 compression Extended 5.25-inch form factor SCSI-2 interface, either single-ended or differential, optional fast SCSI. Compression is DLZ (Digital Lempel-Ziv) "...a head life of 10,000 hours (compared to 2,000 hours for other tape products), a recommended average of 10,000 read/writes per cartridge, and an MTBF of 80,000 hours." Search speed averages 68 seconds Repositioning time 1.3 seconds Hard error rate: 1 x 10**17 bits read Undetected error rate: 1 x 10**30 bits read Serial serpentine (128 tracks), variable block bits/inch: 82,000 Tracks/inch: 256 Recording media: CompacTape (tm) IV 0.5 in x 1,700 ft x .3mi thick Cartridge: 4.1 x 4.1 x 1 inch shelf life: 10 years Height: 3.235 in, width: 5.7 in, length: 9 in Reliability: 80,000 MTBF Media reliability: 500,000 passes in start/stop mode (or an average of 10,000 uses/cartridge)
Subject: [5.12.3] DLT2700 (from DEC) From: Tape random access, seven tape, 1 drive library rack mountable 8-inch form factor includes operator control pannel and LED indicators 400,000 mean mechanical cycles before failure uses a 7 cartridge magazine. Magazine "precheck": 75 seconds per magazine Cartridge load (max): 28 seconds Cartridge unload (max): 30 seconds SCSI command set for robotic commands Subsystem reliability: 30,000 power-on hours Height: 10.4 in, width: 8.7 in, length: 27 in weight: 65 lbs same as the TZ877?
Subject: [5.12.4] DLT2000 (from DEC (now Quantum)) From: Tape CompacTape (tm) III Capacity: 20 GB/cartridge (assumes 2:1 compression) 1.25 MB/sec. (Rodney D. Van Meter), (Peter Van Epp),,, rrohbeck@ufhis.enet
Subject: [5.13] MountainGate (was Metrum) VHS {brief} From: Tape MountainGate 800-556-0222 or 702-851-9393 Phone 702-851-5533 Fax in Europe: Mountaingate Data Systems Linda Radley in the UK +44-1256-464-767 (tel) +44-1256-597-48 (fax) Drive: RSP-2150, 2MB/sec sustained, 4MB/Sec burst ST-120 cartridge holds 14.5 GB ST-160 cartridge holds 18 GB See also robotics Integrated with lots of SW packages, and drive prices have come way down. I think you can now get them for less than $15K. Integrates smoothly with robotics. See for one performance evaluation. Lots of good info there, but keep in mind that the testing was conducted in 1992.
Subject: [5.14] VCR VHS From: Tape This appeared recently in the newsgroup, but I don't know anything about it. This is the widget that takes data in one end and spits out a video signal that you can pipe into your home VCR to use your it for data storage. It's only $350, but, for those of us in the U.S. and Japan, it doesn't work for NTSC VCRs. From: Subject: VTS Tech Specifications for Users Date: Mon Nov 28 09:24:29 PST 1994 X-Gateway: Having received a lot of questions from different users of VTS 1020, I'd like to answer them giving short specifications of this unit. 1. CAPACITY: 4 GB Compressed / 2 GB Uncompressed on one E-180 cassette. The amount of data grows according to the tape length. 2. SPEED: 100 KB/sec for PC/AT 286-16 Mhz 200 KB/sec for PC/AT 386-33 Mhz etc. 3. SOFTWARE: The current version is for DOS. Windows support-DOS Window. Read/Write verification is provided. 4. VIDEO: PAL/SECAM System, VHS Tape Also from the newsgroup a while back: We, AT Systems Inc., are distributors of VCR cassete backup kits (including PC board and software package with 1 year warranty and 2 weeks money back policy), please send all inquiries to my e-mail address (Michael V. Kuzmin,, 4/95) And more recently: Check out a company call Cybernetics in Yorktown, Virginia. They put Sony VCR drives in their own enclosures for backup devices. Contact Thomas Dougherty at (804) 833-9000. (Mike Rothenberg,, 1996/4/1)
Subject: [5.15] 19MM (D1 and D2) {Brief} From: Tape 19mm is 3/4 inch helical scan tape. Two varieties exist, D1 and D2. Both originated from broadcast and/or data recorder applications, where the data/signal was analog in nature. They have been modified for digital use, with error correcting capabilities added. Data rates are in the 8-45 MByte/sec range, with storage capacities in the 25-175 GB range in physically different size cartridges with different length tapes, but all fitting into the same tape drive unit.
Subject: [5.16] ID-1 From: Tape SHMO: I'd like to hear more of people's experiences using these things. Note: I would recommend you talk to people who've used these things before buying one!
Subject: [5.16.1] DATATAPE From: Tape DATATAPE (Pasadena, CA, formerly a division of Kodak), has an ID1 system available, with a HiPPI interface. You can find more info and even give them design feedback at The DCTR-LP400 goes up to 50 MB/sec., the fastest single general-purpose tape drive I know of. Reachable by phone at (818)796-9381 (rdv, 96/8/7)
Subject: [5.16.2] Sony From: Tape Sony makes several models of a D-1-based data drive; the format is generally referred to as ID-1. It comes in different models, with equivalent price tags, that run from 8 to 32 MB/sec. The original machine had a VME interface that was extremely low-level ("any lower and you'd have to turn the spindles by hand," someone said); now there is a HiPPI interface available from a company called TriPlex. I understand the HiPPI interface also adds another layer of ECC to improve the otherwise abyssmal error rate (10^-10 becomes ???). Sony is also supposed to be doing their own SCSI and HiPPI interfaces. I don't know the status nor if they are compatible with tapes from the TriPlex unit (I suspect not). SONY has announced 3 interfaces so far. ;-) DFC-1500 - SCSI interface DFC-1700 - FW-SCSI-2 interface DFC-1800 - 8 bit ECL interface that acts as a "scrollable" buffer. All of the interfaces are fully buffered. They list for 40K-88K. I have used the DFC-1700 for some time. From the standpoint of SCSI functionality it is quite good. It obeys the MT commands and if you wish you can either write to it in "raw" mode or DTF, which is SONY's version of the DD-1 spec. On an HP I get 14+MB/Sec on the DTF side and near 16MB in RAW mode. TriPlex makes an interface that does SCSI,FW-SWCI-2 and HIPPI. The price varies. List for the HIPPI version is in the $130K range. The controller is fully buffered. Myriad Logic also builds boards (VME) and a controller. The controller was demonstrated in Europe this year. It is a HIPPI attached controller built out of their existing products. No good feel for the price, but I would GUESS that it will be less than 90K. It is also fully buffered with 384MB of VSB memory. These are very expensive -- $100K+, but for people with the need, they've got the speed. (, (John Stephens), (Rod Van Meter), (stephen w. poole) (8/95)) Sony's sales literature now (1996/3/22) says they plan to introduce a 64 MB/sec. drive "in the near future". (rdv)
Subject: [5.17] D-2 From: Tape Ampex supports D2. Data rates are in the 15 MByte/sec range. The Ampex tape transport and head system were originally sold through E-Systems (EMASS), who built the storage controller and sold it as the ER-90 and coupled it with Odetics robots. Ampex now makes their own interface for the unit, sold as the DST. They also make their own very fast robotics. The ER-90 is popular with the oil crowd. I don't know if the tapes are interchangeable with the DST. (rdv, 12/94) DD-2 (19mm Data D-2 Format) Ampex DST General: 3 cartridge (cassette) sizes - 25, 75, 165 gigabytes (uncompressed). 15 megabyte/sec. sustained (20 megabyte/sec. burst) transfer rate (per drive). Up to 800 megabyte/sec. search speed (per drive). Smart DD-2 format includes partitioning and system zones to maximize storage efficiency and speed data access. 3 layers of Reed-Solomon error correction, with read-after-write verification and automatic rewrite yield error rate of 1 in 10E15 bits read. Drive(s) dual ported SCSI-2 (16 bit fast, differential). DST 310 Tape Drive: All 3 cartridge (cassette) sizes supported - 25, 75, 165 gigabytes (uncompressed). Rack mount or table top configurations. Single unit price: $120K. Ampex recently (dec. '95 or thereabouts) announced a new tape drive model that's substantially cheaper, ~US$80K. Still 15 MB/sec., but I think it only supports S cassettes. Ampex Corporation 401 Broadway, M.S. 3-46 Redwood City, CA 94063-3199 Inquiry: 415-367-2982 Facsimile: 415-367-3850 Internet: (see also Ampex under autochangers -- they make their own for this tape drive) (, 94/12/23)
Subject: [5.18] StorageTek Helical {Brief} From: Tape Storage Tek has been working on a project called Redwood for a number of years. The cartridge will be 3480 form-factor, to protect users' investment in Storage Tek robotics. ( (Rod Van Meter)) Cartridges come in three lengths, with capacities of 10, 25 and 50 GB. That would put one of their 6,000-cartridge silos up to 300 TB. The ESCON interface is in betatest; SCSI fast & wide due out soon. (, 94/12/19) Reportedly available now (95/5/15) with the SCSI interface; ESCON has been delayed until end of the year. Sustained transfer rate of 11.25 MB/s. Supports compression. List price ~$100K. Compatible with most of the STK robots. See and also autochangers in part 2 of this FAQ.
Subject: [5.19] Optical From: Tape A company called Creo, from Canada I believe, makes a large tape drive that uses ?1"? tape and gets a terabyte of data on a $10,000, 880 meter reel. The time to read the media (media granularity) is huge; at 3 MB/sec. it takes almost four days to read a tape! EMASS have aquired the rights to manufacture the optical tape drive from CREO. The drive ($350k) provides 1TB on line with data transfer at 3MBytes/sec and an average seek time of just 30 seconds. Optical tape media is supplied on 12.5" reels (capacity 1 TByte) by ICI Imagedata in the UK. Expected archival life 30yrs. Typical price of a reel is $8,500. (updated 1995/9/18, has some info.
Subject: [5.20] D-6 {brief} From: Tape From Toshiba & BTS, originally designed as a full-speed (~150MB/sec.) digital HDTV VTR. A model with a HiPPI interface is supposed to be available end of 94. The video version is priced at US$300K+. I believe the tape transport and cartridge are the same as for D-2, though the tape material is different. (4/94, rdv)
Subject: [5.21] D-3 {brief} From: Tape From Martin Marrieta, mentioned here on the net recently. Very fast (10.8 MB/sec.), ~$125K. General availability scheduled for 11/14/94 (9/20/94, I believe the cartridge is the same as Betacam, so look for the broadcast autochanger companies here (rdv).
Subject: [5.22] Sony DTF {Brief} From: Tape Sony DTF is also a helical scan device, utilizing 1/2" digital data cartridges, same form factor as Digital Betacam. Capacitities of 12 (small cartridge) and 42 Gigabytes (large cartridge) UNCOMPRESSED at a sustained transfer rate of 12.2 MB per second again UNCOMPRESSED with and error rate of 10 to the -17. MTBF 200,000 HRS. INLINE sells this as the INLINE RES-400. Cost $55,000 per transport with 16-bit SCSI differential interface. 800.465.4637 or 703.478.0800 main, 703.478.0966 fax (John Tibbitts,, Oct. '95) Also available from Cybernetics, EMASS, Transitional Technology here in the U.S. and several others in Europe and Asia (contact rdv if you're interested in contacts). One of these makes an SBCON interface for the drive. No Fibre Channel or HiPPI yet that I know of. Not available directly from Sony. (updated rdv, 1/96)
Subject: [5.22.1] GY-2120 {New} From: Tape Sony introduced the GY-2120 DTF tape drive in March of 1997. This is a re-engineered version of the first DTF drive, GY-10D. It is now a one piece, smaller and lighter version with added features. Best of all, the new suggested list price is $31,000.00. Features: 12 MB/sec sustained data rate up to 20 MB/sec w/compression 42 GB Native Capacity 108 GB w/compression ALDC High Performance Compression, Average ratio 2.59:1 Automatic Head Alignment Automatic Head Cleaning system Automatic Tape Cleaning system 300 MB/s Search Rate Fast Unload/load of < 25s Head Life > 5,000 hrs MTBF: > 200,000 hrs Read/Write Passes: > 20,000 Tape Archive Life: up to 30 years Distribution has changed as well, we now sell to VAR's and through Sony's Broadcast Division in addition to OEM's: OEM's: Cybernetics TTi EMASS Triplex nStor Precision Echo VAR's: Ovation Data Services Performance Group RFX, Inc. ( (Wes Kuch), 1997/6/24)
Subject: [5.23] DATATAPE DTR-48 {Brief} From: Tape In addition to their ID-1 tape drive, DATATAPE makes a 1/2" tape drive called the DTR-48, 6 MB/sec., 35 GB on a cartridge. I believe the cartridges are the same physical form factor as Betacam. (rdv, 96/8/1)
Subject: [6] Disk From: Disk
Subject: [6.1] CAV, ZCAV and CLV From: Disk Many disks (hard, floppy and optical) run in CAV (Constant Angular Velocity) mode. In this case, the disk spins at a constant rate, and there are the same number of sectors per track on inner and outer tracks. This means that the bits are farther apart on the outer tracks, potentially wasting space. The transfer rate is constant, as the number of bits/track is same and the time/track doesn't vary. CDs (and video laser disks, I believe) and early Macintosh floppies run at Constant Linear Velocity (CLV). That is, the bits are all roughly the same size, and the rotations per minute of the drive is adjust as the head moves in and out. This gives the best areal density of bits, at the sacrifice of seek speed, since every seek requires an adjustment of the rotation speed. The transfer rate is constant, as the size and spacing of bits is constant and the linear velocity is constant. The current rage is ZCAV, Zoned Constant Angular Velocity. Most modern SCSI disks have this feature, and the newest MO drives do, as well. There are a number of zones defined on the disk. The number of sectors per track is different in each zone. Thus, the data is packed more densely than normal CAV, but seek speed is not sacrificed. Another effect of ZCAV is that the media transfer rate varies depending on the head position, because the time/track is constant and the bits/track vary; for example, the Seagate ST12450W Barracuda drive varies from 68 to 113 Mbits/sec, almost a factor of two different. has a couple of papers on this topic, and I (rdv) have a paper in consideration for a conference on the topic (6/96).
Subject: [6.2] Optical {Brief} From: Disk See also Robotics section for library options. Slower than magnetic disks (in general)
Subject: [6.2.1] CD-ROM From: Disk Historically produced off-site at significant first-copy cost but small cost for high volumes. Now on-site 'authoring' systems are available. Standard formats are available. Ads have been posted to the net offering services for as little as US$60 to convert a tape to CD.
Subject: [] DVD (Digital Versatile Disk) (Next-Generation CD) {New} From: Disk Digital Versatile Disk (DVD), the new standard, is a two-layer single or double-sided CD, 8.5 or 17 GB, or double-sided single-layer CD, 9.4 GB. Transfer rate is 11 Mbits/sec (1.4 MB/s). contains a quick overview. First versions will be read only, later will come WORM, then rewritable. First products are slated to be available by the end of 1996. There were two new standards in the works, digital video disk (DVD) and high-density compact disk (HDCD). DVD was proposed by 8 major consumer electronics giants (including Toshiba, with Time-Warner on board) and would have featured a double sided disk capable of storing 5GB of data per side. HDCD, backed by Philips and Sony, would have held 3.7GB data, with the potential to double them up to hold 7.4GB by using a two-layer technology. VHS/Beta wars all over again, along with issues such as backwards compatability to existing CDs, were avoided, thankfully. In December of 1995, everybody agreed on the new DVD format. See the article by Alan Bell in the July 1996 Scientific American. (John Wiest (, (Michael Gold) and others, 95/04/20, rdv, 96/7/1) My (rdv) notes from the Goddard mass storage conference, 1996: Mike Wingart, Sony, talked about DVD. Their data rate is 11.08 Mbps, though video formats are generally used in a slower mode than that. Two sizes, 8 cm and 12 cm. size single layer, double layer, single side double side 8cm 1.4 GB 5.2 GB 12cm 4.7 GB 17 GB track pitch is 0.74 mm, compared to 1.6 for CD (I wrote mm, but I'm sure that's microns). Starts at the inner hub and moves out as it reads the first layer, when it switches to the second it reverses direction. They are working for backward compatibility, but the CD-recordable format uses a dye polymer that's wavelength sensitive; CD-R is 750 nm, but they are using 650 nm laser. Movie is only 4.8 Mbps (he didn't explain the discrepancy, but I presume they just don't use the extra bw). Video is 3.5 Mbps, the rest is audio (5.1 channels, 3 languages, 4 subtitles). They run 130 to 472 minutes of video on 12 cm disks. Using ISO 13346, the volume & file standard for write once and RW non-sequential media. Using ISO 9660, the CD-ROM FS std, needs some modification to work? DVD-ROM spec 1.0 released Sept. 6th, 1996; others coming soon. Rewritable 2.6 GB single layer requires cartridge to protect disk. Cyclability of rewritable media is still an issue.
Subject: [] GIANT CD-ROMS {New} From: Disk A bit of news that I came across recently: GIANT CD-ROMs SLATED FOR 2000 Norsam Technologies Inc. in Albuquerque, N.M., is developing a CD-ROM technology that would enable users to store up to 165 gigabytes on a single disk -- almost 10 times as much data as can be stored on digital video disks. The additional capacity is made possible by replacing the prevailing 800- and 350 nanometer laser writing technology with a more powerful 50-nanometer particle beam. "The Norsam HD-ROM will ... be a major competitor in the high-availability data arena," says the company's president. The HD-ROM disks will be the same size as current CD-ROMs, but will require users to install high-density readers in their devices. (InternetWeek 14 Nov 97)
Subject: [6.2.2] WORM {brief} From: Disk Write-Once-Read-Many Standards are less firm between vendors. For info on file systems for WORM, see the reference to ISO/IEC 13346 in Also check out the OSTA (Optical Storage Technology Association) specs for UDF (Universal Disk Format). UDF is one of the file systems that will be used with DVD. (from and, 1996/3/20)
Subject: [] Sony {brief} From: Disk In the July '95 Wired, p. 56, and seen at SIGGRAPH '95: new Sony WORM drive, looks like 12", maybe bigger. 15GB on a $400 platter. drive is $21K. 76-disk autochanger is $112.5K. ZCAV. transfer rate 2.7 MB/sec. sustained. call 1-800-222-7669. (rdv,7/95)
Subject: [6.2.3] Erasable From: Disk Better standards than WORM
Subject: [] Magneto-Optical Physics From: Disk Magneto-optical disks are plastic or glass disks coated with a compound (often TbFeCo) that has special properties. The disk is read by shining a low-intensity laser (originally infrared, but experiments are being conducted all the way up to blue, I believe; the shorter the wavelength the higher the possible density, all things being equal (which they never are)) onto the media and examining the polarization of the reflected light. To write, a higher-intensity laser is used to heat the material up to its Curie point, where it becomes susceptible to a magnetic field. When the media cools again, its state is "frozen". The polarity of the reflected light during a read depends on the polarity of the magnetic field under which the media was last cooled. Once it has cooled it is no longer suceptible to magnetic fields. Thus, it can be compared in a sense to paleomagnetism.
Subject: [] Sony MiniDisc {Brief,New} From: Disk Sony introduced a 2.5" removable cartridge disk drive in 1993 that will hold 140MB. The rewritable version is magneto-optical; there is also a read-only CD-like version. Also manufactured by others, including Sharp, who says it will have a 700 MB version in 1997. Great info available at or (rdv, 96/7/7)
Subject: [] Magneto-optical, 5.25-inch From: Disk Same number of sectors on each track whether or not track is near center or outer edge. 640 MB. Made by IBM, HP, Sony, Ricoh, others?
Subject: [] Magneto-optical ZCAV, 5.25-inch From: Disk Zoned constant angular velocity - more sectors on outer tracks. GB: 1 ECMA standard 183 going through ISO Fast Track. ADSTAR demonstrated (6/93), San Jose, CA, 408/256-7895.
Subject: [] HP Corsair {Brief} From: Disk 1.3 GB on a double-sided cartridge. See also under MO autochangers in part 2. describes HP products.
Subject: [] Maxoptix T4-1300 From: Disk Does 1.3, 1.0 (read only) and 650 MB media. Max sustained read 2.0 MB/sec. See also under MO autochangers in part 2 for contact info. (rdv, 95/02/14)
Subject: [] Pinnacle Micro {New} From: Disk Pinnacle Micro ( makes MP drives with capacities of 650 MB, 1.3 GB, and 2.6 GB, with transfer rates up to 6 MB/sec(!). Reportedly they're developing a 4.6 GB drive (Apex), too. Pinnacle also makes 10x CD-ROM drives and CD-recordable drives. (rdv, 96/7/8)
Subject: [] Asaca HSMO {Brief} From: Disk My company (Asaca) makes a 12.24 MB/sec. MO drive that uses custom media and two four-beam heads in parallel to increase the transfer speed. Expensive. Call our L.A. office, (310)827-7144
Subject: [] Other Multi-beam MO {None} From: Disk
Subject: [] 3.5-inch MO {Brief} From: Disk Generally looks like a slightly overweight floppy. All current ones are single-sided. First generation 3.5 MO was 128 MB on a cartridge. Second generation devices (available now) are 230 MB. Third generation (due out this year?) will be 650 MB. If they bring the drive price down, could displace floppies as the basic shirtpocket-transportable medium. (rdv,95/1/20)
Subject: [] Sony {Brief} From: Disk Sony now has 650 MB/side 3.5" MO with direct-overwrite capability (a major step forward in MO). See It's ZCAV, and nominally 1-2 MB/s. There's a reasonable discussion of MO physics and technology here, too. ( (Mark Holzbach), 10/95)
Subject: [] Nikon 12-inch MO {Brief} From: Disk Holds 8 GB on a disk, with a transfer rate of ?>1MB/s.
Subject: [] Sony 12-inch MO {Brief} From: Disk Sony also makes a 12" MO. 3.2 GB? (rdv,95/2/7)
Subject: [] NEC 12-inch MO {Brief} From: Disk NEC also makes a 12" MO. (rdv,95/2/7)
Subject: [6.2.4] Electron-Trapping {None} From: Disk
Subject: [6.2.5] Dual Function {Brief} From: Disk Capable of using both WORM and Erasable media. Some do the WORM in firmware -- the media is really rewritable. Others do true WORM. Some drives listed elsewhere, such as MiniDisc, support this.
Subject: [] Panasonic/Toray {Brief} From: Disk The Panasonic/Toray phase-change drive **READS** CD's but **WRITES** phase-change discs which are not compatible with CD's and cost as much as M-O media. (Mike Schuster,, 8/95)
Subject: [] IBM {None} From: Disk
Subject: [6.3] Magnetic From: Disk This area moves WAY too fast for me to keep up with all of the products and announcements; ideally, it should teach enough about principles and other information sources to allow users to find the information they need. Quantum has a good educational web site, with info on the history and technology of disk drives, at A lot of spec sheets for recent disk drives (when they say they also have "old drives", they mean early 90s, not 50s-80s) is available at Looks like a good site.
Subject: [6.3.1] 5.25-inch From: Disk
Subject: [] Seagate From: Disk Seagate's Elite 9 is 9GB -- reports here of backordering, others of availability. Micropolis due out with an 8GB soon? (94/9/1) The fastest (in sustained transfer rate) known 5.25" disk drive is the ST12450W2HP 1.78GB Barracuda drive from Seagate. The Barracuda family is large, so pay attention to the model number! It runs at 68-113 Mbits/sec., depending on head position (it's ZCAV). Assuming that data rate is pre-format, and subtracting 20% for the format overhead, that would be a sustained rate of 6.8-11 MB/sec. Of course, your mileage WILL vary according to transfer size, locality, etc. (rdv,95/2/7) Seagate announced a couple of weeks ago a 23GB disk drive. Reportedly shipping in summer. (Brian A Berg <>, 1996/3/29)
Subject: [6.3.2] 3.5-inch From: Disk
Subject: [] IBM From: Disk The IBM DCMS-310800 Ultrastar2 is 10.8 GB (1GB=10^9) after format, and its sustained rate is fast -- 8.4-14.2 MB/sec (presumably pre-format, so subtract 20%). Only 5400 rpm with an 8.9 msec seek time, so middle-of-the-pack on those numbers. Fast/wide SCSI-2 interface. (rdv,95/02/14)
Subject: [6.3.3] Hard Disk Manufacturers {Brief} From: Disk Here's a partial list of web pages for manufacturers of disk drives. At many of these you can get reasonable tech info and support contacts. (Fujitsu) (now merged w/ Seagate) NOTE: HP announced on about July 10th, 1996 that they're getting out of the hard disk business. The article I saw didn't give an exact time frame. (rdv, 96/7/13) has good info on older drives, and new info is available at
Subject: [6.3.4] Bernouli {None} From: Disk
Subject: [6.3.5] Floptical {Brief} From: Disk I believe flopticals use an optical tracking mechanism to improve ordinary magnetic head positioning and therefore density. The Compaq/3M/Matsushita floptical floppies actually hold 120MB formatted (according to the August 95 Byte), and can read and write standard 1.44MB floppies and read 720KB floppies. (John Brock,, 8/95) Supposed to be available Dec. '95?
Subject: [6.3.6] PC Removables {Brief} From: Disk SHMO -- I haven't followed this too closely. There's the Zip, Jaz, and the new SyQuest.
Subject: [] SyQuest EZ135 {Brief} From: Disk As of August 1995, $199.00 for the drive, $20.00 for each cartridge (135 MB). Removable magnetic hard disk. SyQuest has been in the business for years; the 5.25" removables were popular with Macs. SyQuest has a new 3.5 inch formfactor removable hard drive (due out june). 11msec seek time. Their rep tells me it will list for about $500 and cartridges will come in two flavors: a) 1.3 gig @ $94 (list) b) 650 mb @ $64 (list) (, 1996/3/29)
Subject: [] Iomega Zip {Brief} From: Disk 100 MB/disk, ~$200 for the drive, ~$15-20 for disks. SCSI or parallel interface, 1.5 MB/sec. transfer rate? Don't know anything about the technology, I assume it's simple magnetic hard drive. (rdv, 12/95) I heard that Iomega has licensed the technology to Epson, Fujitsu and one other maker (rdv, 1996/3/29). See
Subject: [] Iomega Jaz {Brief} From: Disk 1 GB, up to 6 MB/sec. xfer rate for a removable hard disk. Drives are $600-$700 U.S. and cartridges $150 for 1GB. See (rdv, 1996/4/10)
Subject: [] SyQuest Removable Cartridge hard Drives From: Disk form factor: 2.5", 42MB form factor: 3.5", 105MB, 14msec ave seek, 3600 RPM, ave sustained transfer rate: 1.3MB/Sec, available in IDE and SCSI versions. Syquest Technology, Inc., 47071 Bayside Parkway, Frement CA 93438, Phone: 800/245- 2278.
Subject: [] Kalok removable cartridge hard drives From: Disk 3.5-inch form factor, 250 MB Phone: 408/747-1315 or 408-468-1800
Subject: [6.3.7] Mainframe {Brief} From: Disk Mainframe disks are sometimes referred to as SLEDs (Single Large Expensive Disks). The term DASD (Direct Access Storage Device) usually refers to a mainframe disk, but is occassionally applied to any hard disk. The WWW FAQ contains some information about mainframe CKD disks and file systems.
Subject: [6.4] Other From: Disk
Subject: [7] RAID {Full} From: RAID {Full} The primary functions of a disk array is to increase data availability, to increase total storage capacity, and to privide performance flexibility by selectively spreading data over multiple spindles. Data Protection - As the number of disks on a system increases, the likelyhood of one failing increases. Thus, a disk array should be immune from a single disk drive crash. Disk mirroring (keeping an exact copy of a one disk on another) is the simplest, but requires twice the disk capacity (and associated cost). Encoding schemes can be used to reduce the redundancy required to lower ratios. Storage Capacity is increased by placing many smaller form factor (5.25 and 3.5-inch) drives onto an intelligent controller which makes all the drives appear as one drive to the computer system. Performance can be increased by spreading data over spindles and performing operations in parallel which allows multiple drives to be working on a single transfer request.
Subject: [7.1] RAID Levels From: RAID {Full} The original taxonomy of RAID levels was published in the SIGMOD paper by Garth Gibson and Randy Katz in 1988 (see below). The taxonomy roughly classifies RAID architectures according to the layout of data and parity information on disks. It is NOT gospel and does NOT cover every possible architecture (it has been pointed out here that that would require an N-tuple showing data block addressing, number and types of parity and ECC information, etc.), but when used properly provides a vocabulary and establishes a framework for discussion. Raid Level 0 - Striping - Data is segmented and split onto multiple spindles. Short Reads - Easily handles multiple simultaneous reads Long Reads - Single operation can be split and processed in parallel Short Writes - Easily handles multiple simultaneous reads Long Writes - Single operation can be split and processed in parallel Redundancy - None Cost - Good (no extra hardware) Raid Level 1 - Mirroring - Duplicate data is kept on multiple splindles Short Reads - Faster (shorter latency) since resolution can be from any of multiple disks Long Reads - Faster since resolution can be from any of multiple disks (*) Short Writes - Slower since need to write to multiple disks Long Writes - Slower since need to write to multiple disks Redundancy - Excellent Cost - Expensive - at least double the spindle cost Raid Level 3 - Data protection disk - mathematical ECC type code calculated from multiple spindles and stored on another spindle. Short Reads - Normal speed (i.e. 1x per-spindle rate) Long Reads - Normal speed Short Write - Slower due to re-calculating of ECC code (including reading from other spindles and the ECC write) Long Write - slightly slower due to ECC writes, but less reading required than in short writes (**) Redundancy - Excellent Cost - only slighly more than no redundancy options Raid Level 4??? similar to 3, with block striping instead of byte. Raid Level 5 - Striping plus data protection - stripe data across multiple spindles (as in RAID Level 0) and have data protection calculations (as in RAID level 3) but don't put all the calculated figures onto one spindle, but spread it out. Short Reads - Normal Long Reads - Faster due to parallelism Short Write - Slower due to ECC calculation (including reading and writing) Long Write - slighly slower due to ECC writes (**) Redundancy - Excellent Cost - only slignly more than no reduncancy options (* should be the same speed as a single spindle) (** -- should be faster than a single spindle due to parallelism on write? somebody help me out --rdv) Benefits of RAID: High data availability (ie, if a single spindle crashes, no data is lost) Increased disk connectivity per system - since multiple spindles appear as one spindle to the computer system. Large capacity storage in a small footprint - Flexibility through intelligent array controllers Performance enhancements in some circumstances. Streamed or Streamified RAID??? (SHMO)
Subject: [7.2] RAID-6 From: RAID {Full} A two-dimensional disk array parity scheme was described by Randy Katz, Garth Gibson, and David Patterson (all then with UC Berkeley - Gibson is now a professor at Carnegie Mellon University) at the 1989 IEEE Compcon conference. This method had one parity calculated along the disk strings and another calculated across them. This would increase the mean-time-to-data-loss by more than 10,000 fold. I am not aware of any implementations of this configuration. Storage Technology Corp (STK - Louisville, Colorado) has described a somewhat similar scheme for their long-delayed Iceberg disk array. This would have a regular, orthogonal RAID 5 parity across drives along with a Reed-Solomon encoding on another drive. This is sometimes referred to as RAID 6 or RAID 5+. STK claims their design will allow failure of ANY TWO drives - which is beyond the survival capabilities of standard RAID 5. A RAID 5 which is 'deep' can survive failures in more than one drive so long as it doesn't lose more than one drive per rank: HBA1 HBA2 HBA3 HBA4 HBA5 HBA6 HBA7 HBA8 | | | | | | | | Rank1 Disk1 Disk2 Disk3 Disk4 Disk5 Disk6 Disk7 Disk8 | | | | | | | | Rank2 Disk9 Disk10 Disk11 Disk12 Disk13 Disk14 Disk15 Disk16 . . . . . - etc. Rank4 . . . . Disk32 If the above is a RAID 5 then losing drives 5 & 6 will destroy data. If it is a RAID 6 then it will not. Losing drives 3 and 12 will not disable a RAID 5 nor a RAID 6. But RAID 6 will cost more and may have slower performance for small random writes from having to update more parity data. I think there are clearly ways to mitigate the parity update perfomance for RAID 6 as well as RAID 5. -- Dick Wilmot Editor, Independent RAID Report (510) 938-7425
Subject: [7.3] John O'Brien and RAID-7 From: RAID {Full} RAID-7 is a marketting term created by Storage Computer, Inc. for what others here have described as RAID-4 with a write cache. John O'Brien (, (their marketting manager?) frequently posts here. His claims of ~10x improvement on I/O rates for VAXes have been shown to be poorly measured; the change in systems was not simply a RAID-for-modern-disk swap, but included increasing the CPU power by a factor of three and eliminating the HSC and old disk technology. He has also made difficult-to-substantiate claims about the growth and market success of his company relative to competitors. Thus, wise advice would be to take everything Mr. O'Brien says with a grain of salt (not bad advice for dealing with anyone, but especially true for dealing with vendors). The debate also appears here frequently as to whether or not you really WANT your RAID array doing write cacheing; Unix file systems may depend on specific ordering of writes and otherwise make assumptions that could leave you in trouble with power or disk failures. If write ordering is preserved, the danger is somewhat mitigated. That said, some posters here are pleased with their RAID7 arrays, and although opinion runs prevalently against Mr. O'Brien himself (and lately his pal Michael Willett who interestingly is quoted here from before he worked for Storage Computer), the possibility exists that the product is worthwhile.
Subject: [7.4] RAID Papers From: RAID {Full} (Berkeley FTP pointers updated, 95/5/11) A nice collection of RAID papers was published in the Fall, 1991 issue of _CMG Transactions_. A few more appeared in the December, 1992 _CMG Proceedings_ and there are 3 RAID papers in the 1993 International Symposium on Computer Architecture (Published as _Computer Architecture News 21_, #2, May, 1993 by ACM SIGARCH. (, Dick Wilmot, Editor, Independent RAID Report) There is a short RAID FAQ at (rdv, 96/2/21) Try contacting the RAID project at the University of California, Berkeley. In the proceedings of the recent IEEE Mass Storage Symposium, Ann Drapeau and Randy Katz have a paper describing the reults of some investigations into the use of tape arrays. I think you can find RAID papers, perhaps this one, on anon ftp at Have no address for Ann Drapeau, but Randy Katz is Some of the RAID papers are available via anon ftp from Ann Drapeau's email address is (, Mike DeVaney) (, Edward K. Lee) >>I am looking for papers or technical papers on RAID... You could get that lengthy RAID taxonomy research report from Storage Computer as mentioned recently on these news groups, by Emailing them at Alternatively, their phone number is 603 880 3005. I do not know if their RAID research report is copyrighted or not. I believe their executive in charge of RAID activities in Hong Kong would be John Taylor, the former Wang national accounts director. They also put on technical raid seminars which might be of interest to your PhD students, concentrating on performance enhancements over RAID 3/4/5 (somewhat less than an order of magnitude, but I have not reviewed their benchmark data.) The RAID theory discussed is rather interesting. (MICHAEL.WILLETT@OFFICE.WANG.COM, Michael Willett) --------- >> I am looking for papers or technical papers on RAID or other multiple disks >> storage systems. Could somebody give me pointers for them? Here are some papers that I either have read or am looking for: I don't have copies of this group: Dishon, Yitzhak; Lui, T.S.; Disk Dual Copy Methods and Their Performance; FTCS-18: Eighteenth International Symposium on Fault-Tolerant Computing, Digest of Papers p 314-318 Gray, J.N. et. al., Parity Striping of Disk Arrays: Low Cost Reliable Storage With Acceptable Throughput, 16th International Conference on VLDB (Austrailia, August 1990) Katz, R.H.; Patterson, D.A.; Gibson, G.A.; Disk System Architectures for High Performance Computing; Proc. IEEE v 78 n 2 Feb 1990 Muntz, Richard R.; Lui, John C.S.; Proformance Analysis of Disk Arrays Under Failure; Proceedings of the 16th International Conference on Very Large Data Bases (VLDB); Dennis Mcleod, Ron Sacks-Davis, Hans Schek (Eds.), Morgan Kaufmann Publishers, Aug 1990 pp 162-173 Ng, Spencer; Some Design Issues of Disk Arrays; Compcon '89: Thirty-Fourth IEEE Computer Society Internationsl Conference p 137-142 DISK ARRAYS, STRIPING, SPINDLE SYCHRONIZATION Ng, Spencer W.; Improving Disk Performance via Latency Reduction; IEEE Transactions on Computers v 40 1 Jan 1991 p22-30 LATENCY REDUCTION, ROTATION LATENCY, DISK PERFORMANCE Reddy, A.L. Narasimha; Banerjee, Prithviraj; Performance Evalutaion of Multiple-Disk I/O Systems; Proceedings of the 1989 International Conference on Parallel Processing p 315-318 Here are some good papers on disk arrays with emphasis on RAID: Chen, Peter M.; Gibson, Garth A.; Katz, Randy H.; Patterson, David A.; Evaluation of Redundant Arrays of Disks Using an Amdahl 5890; 1990 ACM SIGMETRICS Conference on Measurement & Modeling of Computer Systems p 74-85 Chen, Peter M.; Patterson, David A.; Maximizing Performance in a Striped Disk Array; Proceedings of the 17th IEEE Annual International Symposium on Computer Architecture p 322-331 Chen, Shenze; Don Towsley; Performance of a Mirrored Disk in a Real-Time Transaction System; 1991 ACM SIGMETRICS Conference on Measurement & Modeling of Computer Systems p 198-207 Chervenak, Ann L.; Katz, Randy H.; Performance of a Disk Array Prototype; ACM SIGMETRICS 1991 Conference Proceedings p 188-197 Menon, J.; Mattson, R.L. and Spencer, N.; Distributed Sparing for Improved Performance of Disk Arrays; IBM Research Report RJ 7943 (Jan. 1991) Patterson, David A.; Chen, Peter; Gibson, Garth; Katz, Randy H.; Introduction of Redundant Arrays of Inexpensive Disks (RAID); Compcon 1989: Thirty-Fourth IEEE Computer Society International Conference p 112-117 Schulze, Martin; Gibson, Garth; Katz, Randy; Patterson, David A.; How Reliable is a RAID; Compcon '89: Thirty-Fourth IEEE Computer Society International Conference p 118-123 (, Dan Jones) -------- >>I am looking for papers or technical papers on RAID... A good set of the Berkeley papers are available via anonymous FTP. If I remember, the machine was Also, an archie search on "RAID" would probably turn up a nice on-line collection of information. (sorry, not at an Internet site to check this right now...) ( , Lester Buck) Further Information: %A Garth Gibson %A Randy H. Katz %T A case for redundant arrays of inexpensive disks (RAID) %C Proc. SIGMOD. %c Chicago, Illinois %D 1--3 June 1988 %P 109 116 %k RAID, disk striping, reliability, availability, performance %k disk arrays, SCSI, hardware failures, MTTR, MTBF %k secondary storage %L Jacobson has a copy %x Increasing the performance of CPUs and memories will be %x squandered if not matched by a similar performance increase in %x I/O. While the capacity of Single Large Expensive Disks (SLED) %x has grown rapidly, the performance improvement of SLED has been %x modest. Redundant Arrays of Inexpensive Disks (RAID), based %x on the magnetic disk technology developed for personal %x computers, offers an attractive alternative to SLED, promising %x improvements of an order of magnitude in performance, %x reliability, power consumption, and scalability. This paper %x introduces five levels of RAIDs, giving their relataive %x cost/performance, and compares RAID to an IBM 3380 and a %x Fujitsu Super Eagle. (
Subject: [7.5] R-Squared {Brief} From: RAID {Full} Vangard Disk Array for DEC, Sun, HP, IBM RS/6000, SGI and others Address: 11211 E Arapahoe Rd., Suite 200, Englewood, CO 80112 Phone: 303/799-9292, Fax: 303/799-9297
Subject: [7.6] Sun {Brief} From: RAID {Full} Sun Microsystems has a new Fibre Channel array that does RAID 0, 1, and 5. See http://WWW.Sun.Com under the products descriptions. (rdv,94/8/8)
Subject: [7.7] Clariion {Brief} From: RAID {Full} See A division of Data General. Mostly big systems, I believe.
Subject: [7.8] BayDel {Brief, New} From: RAID {Full} Targetted at Unix systems -- Sun, HP, SGI, etc. See Fairly big vendor, I'm told. (rdv, 97/3/18)
Subject: [7.9] the RAIDbook {Brief} From: RAID {Full} The RAIDBook, a 100+ page tutorial on RAID technology and the RAID Advisory Board, is available from Technology Forums, LTD, of 6931 Glenview Lane, Lino Lakes, MN 55014-1296. Contact Joe Molina, President of Technology Forums at <XXX> (phone numbers no longer valid?) (rdv,97/3) I've read it, it's decent but a little repetitive. Defines many low-level terms of interest only to those who need to know the internals. (rdv,95/2/7)
Subject: [7.10] Software Striping {Brief} From: RAID {Full} Silicon Graphics provides software striping of SCSI disks; thus your host can effectively act as a RAID controller, providing flexibility and probably reduced price, possibly with a performance penalty in the form of increased CPU overhead. However, it probably means that it can spread the I/O load over multiple I/O controllers. (similar features in other systems? SHMO --rdv) RAID0 is in late beta under Linux. ( (Gjoen Stein), 95/10/6) sdsadmin on the HP 7xx line does raid 0 striping and works well. this is also apparently possible on the 8xx machines using LVM. sdsadmin is due to disappear with hpux 10, replaced by LVM. I believe the Advanced FS on Alphas can also do raid 0. (mark hahn,, 94/11/17) ATTO Technology has ExpressStripe, which does software striping on a Mac. Cyranix makes EZRAID PRO (RAID 0,1,4,5) for OS/2. Voice: +1 613 738 3864 Fax: +1 613 738 3871
Subject: [7.11] RAID Vendors From: RAID {Full} RAID vendors come and go quickly, OEM each other's equipment, change names, and other activities that seem aimed at simply obscuring the market. No list like this could be complete and up to date for long; I'll gladly take updates. See for one good list of RAID vendors, and for another. Other reviews are available at, and ( (Steven Hessing), 1996/3/30) The November '94 issue of _Advanced Imaging_ has a big article on storage, primarily RAID arrays, with a pretty comprehensive list. This table is distilled from that. Most of the info appears to be from the vendors themselves. Almost all of these are fast/wide SCSI; a few are Fibre Channel, NuBus, PCI or HiPPI (usually with IPI-3 command set). Most of these vendors have more than one model, only a few are listed here. (rdv,95/1/18) Most of these have some web presence; a Lycos search would turn up their sites. PC = Personal Computer (IBM compatible) MC = Macintosh PS = PC Server (Netware, NT et al) NT = Windows NT UX = Unix (generic) PU = Personal Unix WU = Workstation Unix & workstation servers MF = mainframe MI = minicomputer (AS/400) SU = Supercomputer FC = Fibre Channel interface (usually SCSI command protocol) Maker Model RAID Levels Uses ------------------------------------------------------------------------- AC Technology Concorde 0,3,5 WU ADJFILE Systems Cougar, Tiger 0,1,3,5 ?? ANDATACO GigaRAID 0,1,3,5 UX,NT AT&T Global Information Series 3 ?? WU,PS,PC Systems -- NCR BusLogic DA-x988 0,1,3,5 PC,PU,PS (PCI) Canary Communications IDA3500 0,1,3,4,5 ?? Ciprico 6800 Real-Time ?? ?? RAID Array Cybernetics Xtreme 0 ?? DEC StorageWorks 0,1,5 ?? RAID Array 210 Distributed Processing SmartRAID 0,1,5 PC,PU,PS Technology DynaTek Automation AddARRAY 0,1 ?? Systems Fujitsu Comp. Prod. DynaRAID ?? ?? America FWB, Inc. SledgHammer*FT 5 MC IBM Storage Systems 7137 Disk Array 0,5 WU Legacy Storage Systems SmartArray ?? PC (PCI) Maximum Strategy Gen5 Storage 0,1,3,5 SU (HiPPI,FC) Server Mega Driver Systems MR & MK Series 0,3,5 PC,PU,PS,MC,WU MicroNet Technology RAIDbank Plus 0,1,5 PC,PS,MC,PU? Micropolis RAIDION,GANDIVA ?? PC,MC,PS,PU,WU Microtech Int'l XLerator 0,1 MC Mylex DAC960S 0,1,5,6?,7? ?? Procom Technology LANForce-5 0,1,3,5 MC,?? Raidtec FlexArray IX 0,1,3,5 ?? Recognition Concepts RDR series ?? ?? Storage Computer RAID 7 7?(4?) ?? Storage Concepts Concept 910 ?? ?? Storage Tek Iceberg ?? MF XL/Datacomp 9638 5 MI,WU
Subject: [8] Solid State Disk (SSD) Frequently Asked Questions (FAQ) From: Solid State Disk (SSD) Frequently Asked Questions (FAQ) *Note: This section is a slightly trimmed and editted version of the SSD FAQ from Robert at DES ( which I think he also posts to c.d.sybase. I would take the "up to 1000 times faster" claim with a grain of salt, though the general info is good. --rdv, 94/9/15 1) Q. What are solid-state disk emulators? A. Simply put, solid-state disk emulators are Dynamic Random Access Memory (DRAM)-based storage devices that appear to the host exactly as a magnetic rotating disk. DRAM chips, which are ultra-fast devices that store data while the system is on, increase data access, thereby eliminating I/O bottlenecks that constrain overall system performance. Solid-state disk emulators can be either volatile or non-volatile, meaning that they are able to retain data when the system is turned off. DRAM alone is volatile. Solid-state disk emulators that are designed with an integrated backup system are non-volatile storage devices; if a power outage occurs, the user's data is protected by the backup system and will not be lost. Solid-state disk emulators are volatile when methods for backing up data are absent. A power failure will cause data to be lost on a volatile solid-state disk. 2) Q. How do solid-state disk emulators work? A. Solid-state disk emulators plug into a computer's I/O controller. Typical client/server systems use the ANSI-standard SCSI interface on its I/O controller. It is plug-and-play because it emulates a rotating disk. No special drivers or operating system patches are required to make it work. In addition, because there are no moving parts, seek and rotational latency times are zero, which aids solid-state disk emulators in performing up to 1000 times faster than magnetic rotating disk drives. 3) Q. What applications are well-suited for Solid State Disk? A. In general terms: 1) transaction processing, 2) batch processing, and 3) query or decision support analysis. Many types of application software can take advantage of the super-fast access times SSD offers. 4) Q. How reliable are Solid State Disks? A. Based on real world user data from a large SSD site, the actual power on hours mean-time between failure is greater than 1,000,000 hours. Since this site has yet to have a failure, the number is likely to go up.
Subject: [9] Other Devices From: Other Devices
Subject: [9.1] Holographic Storage Products {Brief,New} From: Other Devices Holoplex is a startup company doing holographic memories. Info on the web at They reportedly have a 100-image store available as a product. (rdv, 96/7/23) Tamarack Storage Devices, Inc, a spin-off from Microelectronics and Computer Technology Corporation (MCC), is developing with Projectavision Inc. to produce a product with ten times greater storage densities than magnetic and 10 to 1000 times faster than floppies, tapes, and CD-ROMS. First products expected first quarter 1994. (Ref: MCC Collagorations Newsletter, Volume 3, No. 1; Spring 1993) ( Note: obviously Tamarack hasn't changed the storage world yet; anybody know how they're doing? They were awarded another $10.7M by ARPA in 1995 for continued research, but I can't even find a web page for them. (rdv, 96/7/23) Also another report of experiments at Stanford recently (8/94). Scientific American in the Nov. 95 issue reportedly has an article about holographic storage, but I haven't tracked it down yet. BYTE Magazine - April 1996 Good Cover Story on "Holographic Storage" The trade journal "Data Storage" for May/June 1996 had an article on holographic storage. Reportedly there is work going on at Georgia Tech on 3-D liquid crystal data storage, producing a possible gain of 3 orders of magnitude. (rdv, 1996/3/29, from HPCWIRE)
Subject: [9.2] TeraStor {Brief, New} From: Other Devices Big splash and a bunch of announcements March '97. Apparently they've developed a technique for putting the laser optics for a magneto-optical drive onto the slider for a regular magnetic head, giving better density to MO products. Company's still young and needs lots of people, but it's experienced storage guys. I think their suggestion that they'll have products in early '98 is probably optimistic. See (rdv,97/3/18)
Subject: [10] RAIT (Redundant Arrays of Inexpensive Tape) From: RAIT (Redundant Arrays of Inexpensive Tape) (6/93) There are several tape array products on the market: Data General is selling the CLARiiON Tape Array Subsystem comprising between five and seven 4mm DAT tape drives. Data can be recorded in RAID-like striping redundancy, mirrored, or in conventional DAT layout. This unit can provide up to 30GB of unattended contiguous storage. The tape drives can record at sustained rates of 183 - 732 KB/second each but customers should expect sustained backup at around 1 megabyte/second of compressed data after accounting for host overheads. Data General is working on a seven tape caddie to hold tape sets together. It is essential that tapes in a RAID group not be separated. NCR announced a tape array software product for NCR uniprocessors and System 3450, System 3550 and StarServer Systems running UNIX V R4.2.01. This tape array software yields faster and more reliable backup of large database and file servers than with any single tape drive available today but uses customers existing tape devices. It writes simultaneously to multiple drives and can use array techniques to recover from loss or failure in any single tape. The motivations for tape arrays seems to parallel those for disk arrays: - higher bandwidths - increased reliability (, Dick Wilmot, Editor, Independent RAID Report) (6/93) Pick up any DEC related trade rags and you can find an ad for an 8mm tape array. The ad I just found is by Contemporary Cybernetics and uses two five GB 8mm drives with compression - they CLAIM to be able to get 50 GB os storage total - but how many customers have 50 GB worth of 5:1 compressible data? Anyway - the ad doesn't mention RAID, but they support RAIDish (!) features such as striping and mirroring. It also supports offline tape-to-tape copy and will automatically cascade onto the second tape when the first one fills (useful for utilities that can't deal with multi-drive/multi- volume). I SEEM to remember someone having something like this with more drives, but of course I couldn't locate the ad. I would be really interested in seeing something like this for 3480 since the transfer rate is already quite high... (, Tom Bodoh) At the Monterey IEEE Mass Storage Conference in April '93, Ann Drapeau from Randy Katz's group presented a paper on striped tape. The National Storage Lab High Performance Storage System reportedly supports striping of removable media in the system software. (rdv,95/1/13) Something that came through the newsgroup recently (95/2/5): Tape Arrays High Performance tape drive units for large networks and minis. Fast: up to 4Megabyes/second High Capacity: from 24Gb on 4mm DATS to 60GB on DLTs; with autoloaders,up to 616GB Flexibility: Stripe data across 4 drives, mirror data, stripe 2/mirror 2 - double your speed while creating an off-site storage copy; off-line copy; pass-thru mode, etc. Transparent to your backup software - no changes or retraining Compatible with all major OSs; including Novell, WindowsNT, Unix, Sun, HP, Silicon Graphics, VMS, etc. For More information: William Wirth Just spotted this in a PC rag. Andataco can stripe, mirror or RAID DLT, 8mm or 4mm. Check out or call 800-334-9191 or +1-619-453-9191. Or email (Andataco is an integrator for numerous storage products including RAID arrays.) Compaq now has a DLT tape array. Some specs available at Stripes or does RAID 5. (rdv, 96/4/17) Tecmar makes a tape array with up to 30 (custom) drives. A "rotating" spare is used to gradually back up the entire system. (Georg Feil,,, 96/10/17)
Subject: [10.1] DataVast (was VastNSS) From: RAIT (Redundant Arrays of Inexpensive Tape) Originally developed at our institute for use in radio astronomy, the DataVast is now being built and marketed by DataVation. DataVast is an SVHS tape array with up to 30 tape transports and a capacity of 50 GBytes uncompressed per tape (1.5 TB total with 30 transports). DataVast is best suited for near-line networked applications. It sits on an Ethernet network and acts as an NFS file server. An internal 4 GB disk serves as a cache for recently accessed files. Except for the fact that files often take longer to access, the system appears exactly like an extremely large disk. File "seek" times depend on user access patterns and file sizes, but most users can expect average access times under 1 minute and worst-case access times under 3 minutes. Data transfer rates are comparable with typical Ethernet NFS servers. DataVast is not redundant in the sense of a RAID -- the array architecture is used to increase capacity and reduce cost (the main electronics is replicated only once for up to 30 tape transports, unlike SCSI RAIT systems where each tape drive duplicates all electronics). There is no robotics. See VastNSS is Vast Network Storage Server. This was known as VastNSS, owned by Legacy, but some of the guys split and bought the technology and founded Datavation, and renamed the product DataVast. (rdv, 97/3/18) (info updated courtesy of Michael Mansell,, 97/3/18)
Subject: [11] RAOT (Redundant Arrays of Other Things :-) From: RAOT (Redundant Arrays of Other Things :-) Pinnacle Micro has been advertising what they call the Orray -- essentially RAID done with removable magneto-optical disk drives. They claim sustained transfer rates up to 8 MB/sec., which seems implausible given that it's only four drives, and even HP MO drives are below 2 MB/sec. sustained. Apparently no redundancy in the system for that configuration (so I guess my ROAT designator is a misnomer), but it should be generally less necessary for MO than magnetic disk (drive failures normally don't result in the destruction of data or media). --rdv, 94/7/20

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