ITEM: F3418L

Questions on LVM.

Question:

Aix level 3.2.3. Customer has question on what are the implications of
my database overwriting the 512 byte LVCB (logical Volume Control Block).

Response:

By writing over the LVCB, you will cause a couple of minor problems:

When you import the volume group with importvg, the import command
will update the VGDA of the volume group with information from the LVCB.
Since there isn't a LVCB on the lv in question, you will get
the following errors trying to import the volume group:

  0516-520 updatelv: Partially successful with updating logical
        volume otestlv.
  0516-556 synclvodm: Unable to update logical volume otestlv.
  0516-782 importvg: Partially successful importing of hdisk1.

Any logical volumes that do not have an LVCB will not be updated
in the VGDA, and so your VGDA will not contain valid information
about any lv's of this type.

If you try to change the logical volume, for example to make the
inter-policy maximum instead of minimum, the change will be written
into the ODM, but will not be updated in the LVCB. You will get the
following error:

  0516-622 extendlv: Warning, cannot write lv control block data.

The infromation you changed will be preserved so long as you do not
export the volume group. When you export and reimport the volume group,
this information will return to the default. This does not seem to
be a problem for any attributes that need to remain the same, like size
or maximum partitions.

You can run your system with your database writing over the LVCB, but
it is still recommended that you skip the first 512 bytes if possible
and most databases seem to offer this capability.



Support Line: Questions on LVM. ITEM: F3418L

Dated: December 1993 Category: N/A

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