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comp.unix.aix Frequently Asked Questions (Part 3 of 5)
Section - 1.703: Chlv warning. Is the first 4k of a LV safe?

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Top Document: comp.unix.aix Frequently Asked Questions (Part 3 of 5)
Previous Document: 1.702: How do I make a filesystem larger than 2Gb?
Next Document: 1.704: What's the limit on Physical Partitions Per Volume Group?
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The first 4k of a raw LV are used to store control block.
Applications that write to the raw disk can overwrite this section
(common applications that do this are Oracle and Sybase).  Commands
that call getlvcb will generate a warning but succeed (since the
control block exists in ODM.  Don't run synclvodm unless you really
want to erase the first 4k and replace it with the info from the ODM.

shieh@austin.ibm.com (Johnny Shieh) has kindly provided the following
explanation:

The logical volume control block (lvcb) is the first 512
bytes of a logical volume.  This area holds important
information such as the creation date of the logical volume,
information about mirrored copies, and possible mount points
in a journaled filesystem.  Certain LVM commands are required
to update the lvcb, as part of completeness algorithms in
LVM.  The old lvcb area is first read and analyzed to see if
it is a valid lvcb.  If the information is verified as valid
lvcb information, then the lvcb is updated.  If the
information is not valid, then the lvcb update is not
performed and the user is given the warning message:

	Warning, cannot write lv control block data

Most of the time, this is a result of database programs
accessing the raw logical volumes (and thus bypassing the
journaled filesystem) as storage media.  When this occurs, the
information for the database is literally written over the lvcb.
Although this may seem fatal, it is not the case.  Once the
lvcb has been overwritten, the user can still:

	1) Extend a logical volume
	2) Create mirrored copies of a logical volume
	3) Remove the logical volume
	4) Create a journaled filesystem with which to mount
		the logical volume (note that this will destroy any
		data sitting in the lvcb area)

However, there is a limitation caused by this deletion of the
lvcb.  The logical volumes with deleted lvcb's face possible,
incomplete importation into other AIX systems.  During an
"importvg", the LVM command will scan the lvcb's of all defined
logical volumes in a volume group for information concerning the
logical volumes.  Surprisingly, if the lvcb is deleted, the
imported volume group will still define the logical volume to
the new AIX system which is accessing this volume group, and
the user can still access the raw logical volume.  However, any
journaled filesystem information is lost and the logical volume
and its associated mount point won't be imported into the new AIX
system.  The user must create new mount points and the availability
of previous data stored in the filesystem is NOT assured.  Also, during
this import of a logical volume with an erased LVCB, some non-jfs
information concerning the logical volume, which is displayed with
the "lslv" command, cannot be found.  When this occurs, the system uses
default logical volume information to populate the logical volume's
ODM information.  Thus, some output from the "lslv" will be inconsistent
with the real logical volume.  If logical volume copies still exist on
the original disks, this information will not be correctly reflected in
the ODM database.  The user should use "rmlvcopy" and "mklvcopy" to
rebuild any logical volume copies and synchronize the ODM.  Finally,
with an erased lvcb, the output from the "lslv" command might be
misleading or unreliable.


User Contributions:

But remnants' crop burning hits harvesting hard

This sunday, quite possibly 28, 2019 snapshot, Provided by the city service group, jointly for Jarniyah, contains been authenticated based on its contents and other AP reporting, Shows Syrians lifetime extinguish a fire in a field of crops, wearing Jaabar, Raqqa state, Syria. Thousands of acres of wheat and barley fields in both Syria and Iraq have been scorched by the fires within harvest season, that typically runs until mid June. "The life that we live here is already bitter, " stated Hussain Attiya, A farmer from Topzawa Kakayi in upper Iraq. "If the outcome continues like this, I would say that no one will continue to be here. I plant 500 to 600 acres on a yearly basis. still, I won't be able to do that because I can't stay here and guard the land day and night. "ISIS militants have a history of working with a "Scorched earth insurance coverage " In areas from that they can retreat or where they are defeated. Ahmed al Hashloum thoughts Inmaa, Arabic for benefits, A local civil group that supports farming. all it takes is a cigarette butt to set haystacks on fire, He brought up. Said the fires are threatening to disrupt normal food production cycles and potentially reduce food to protect months to come. The crop burning remains localized and can't be compared to pre war devastation, Beals considered that. "suffice to say, It is only the beginning of the summer and if the fires continue it could lead to a crisis, " Beals recounted,AlternativeHeadline,prepared crop burning blamed on ISIS remnants compounds misery in war torn Iraq and Syria"}

But good news is short lived in this part of the world, Where residents of the two countries struggle to face seemingly never ending violence and turmoil amid Syria's civil war and attacks by remnants of the Islamic State of Iraq and Syria (ISIS) social groups. of course, Even in locations where conflict has subsided, Fires currently raging in farmers' fields, depriving them of valuable crops.

The blazes have been blamed also consider on defeated ISIS militants seeking to avenge their losses, Or on Syrian regime forces battling to rout other armed groups. Thousands of acres of wheat and barley fields in both Syria and Iraq have been scorched by the fires within harvest season, what kind runs until mid June.

ISIS militants have a history of implementing a "Scorched earth guideline" In areas from which retreat or where they are defeated. this "A means of inflicting a collective punishment on those put aside, said Emma Beals, a completely independent Syria researcher.

ISIS militants claimed obligations for burning crops in their weekly newsletter, al Nabaa, Saying they targeted farms owned by senior officials in six Iraqi provinces and in Kurdish administered eastern Syria, sending the persistent threat from the group even after its territorial defeat.

ISIS said it burned the farms of "The apostates in Iraq together with the Levant" And required more.

"It seems that it'll be a hot summer that will burn the pockets of the apostates as well as their hearts as they burned the Muslims and their homes in the past years, this great article said.

countless acres of wheat fields around Kirkuk in northern Iraq were set on fire. Several wheat fields in the Daquq district in southern Kirkuk burned for three days straight yesterday.

In eastern Syria's Raqqa state, Farmers battled raging fires with items of cloth, bags and water trucks. Piles of hay burned and black smoke billowed above the job areas.

The Syrian Observatory for Human Rights said through 74,000 acres (30,000 hectares) linked farmland in Hassakeh, Raqqa and completely to Aleppo province to the west, Were scorched.

Activist Omar Abou Layla said local Kurdish led forces failed to react to the fires in the province of Deir el Zour, Where ISIS was uprooted from its last property in March, (...)

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Top Document: comp.unix.aix Frequently Asked Questions (Part 3 of 5)
Previous Document: 1.702: How do I make a filesystem larger than 2Gb?
Next Document: 1.704: What's the limit on Physical Partitions Per Volume Group?

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