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comp.arch.storage FAQ 1/2
Section - [5.12] DLT {full}

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From: Tape

See http://www.quantum.com/support/bulletins/tape.html for info on
current issues concerning DLT.

Also see the DLT FAQ, maintained by Larry Kaplan,
lkaplan@tdh.qntm.com. For Suns, there is info at
ugle.unit.no:info/unix/DLT_on_Sun.txt.


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 http://www.quantum.com/products/menus/tape.html for specifications,
http://www.quantum.com/support/faq/dltfaq.htm for some FAQ answers. I
also have an old copy of Larry Kaplan's different FAQ available at
http://alumni.caltech.edu/~rdv/comp-arch-storage/dlt-faq.html.

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".

>michelotto@mvxpd5.pd.infn.it (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.

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