Recreate lvcb

[RudiVVC]

Hi!

I don't know why, but one of our logical volume control blocks has gone.

For example:
getlvcb -ATi prd_oradta

shows no results.

Another logical volume owns a control block.
IBM support says, that there is no way to recreate it.

Although all needed information can be found within the ODM there is no way to get the lvcb back, except: delete
and recreate the whole logical volume.

Is this correct? When will I get in trouble because of the missing control block?

bye
Ruediger

 

[ogniemi]

If you are using LV as a raw device then LVCB could be overwritten (1st 512 bytes of first 4kb block in LV). (I had a similiar problem with database-log on raw device - creating it LVCB was overwritten and now I get warnings that LVCB is not there). For my application it is not a problem - problem would be if I would recreate the LVCB - then my database would fail)

Are you sure you need to recreate LVCB???


Here is some information from docu:

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 the journaled filesystem (JFS). Certain Logical Volume Manager commands are required to update the LVCB, as part of the algorithms in Logical Volume Manager. The old LVCB is read and analyzed to see if it is a valid. If the information is valid LVCB information, the LVCB is updated. If the information is not valid, the LVCB update is not performed and the following warning message is issued: Warning, cannot write lv control block data

Most of the time, this is a result of database programs accessing raw logical volumes (and bypassing the JFS) as storage media. When this occurs, the information for the database is literally written over the LVCB. Although this might seem fatal, it is not the case. Once the LVCB is overwritten, you can still do the following:


Expand a logical volume

Create mirrored copies of the logical volume

Remove the logical volume

Create a journaled filesystem to mount the logical volume.
There are limitations to deleting LVCBs. The logical volumes with deleted LVCB's face possible, incomplete importation into other AIX systems. During an importvg, the Logical Volume Manager command scans the LVCB's of all defined logical volumes in a volume group for information concerning the logical volumes. 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 you can still access the raw logical volume. However, any journaled file system information is lost and the associated mount point will not be imported into the new AIX system. You must create new mount points and the availability of previous data stored in the filesystem is not assured. Also, during this import of logical volume with an erased LVCB, some non-jfs information concerning the logical volume, which is displayed by the lslv command, cannot be found. When this occurs, the system uses default logical volume information to populate the logical volume's ODM information. Therefore, some output from lslv will be inconsistent with the real logical volume. If any logical volume copies still exist on the original disks, the information will not be correctly reflected in the ODM database. Use rmlvcopy and mklvcopy commands to rebuild any logical volume copies and synchronize the ODM


r,m.