ITEM: S5984L

Sysback error with raw LVs missing LVCBs

Question:

Env:    AIX/6000 3.2.5, Sysback/6000 ver 3 

Desc:   Customer is running Sysback and gets this error:
        Copies x LPs does not match the number of physical partitions

        There is no mention of where the error is coming from.

Action: This error comes as a result of an inconsistency between
        the actualy structure of a logical volume and its entry
        in the ODM.  This occurs in Sysback in the mkvginfo and
        getlvminfo scripts.

        We first synchronized each volume group with:
        \# syncvg -v VGname
        \# synclvodm -v VGname

        To isolate where the problem is coming from, we ran
        "ksh -x /usr/sbin/mkvginfo -S -f rootvg".  With the "-S"
        flag, Sysback will check EACH volume group and EVERY
        logical volume, whether or not it is a filesystem.

        In this case, it returned the error on the line
        "+ makelvrec indb0".

        indb0 is a raw logical volume used by Informix in volume
        group cmgvg.  We ran the following on indb0:
        \# lslv -m indb0  (check mirroring, anything missing?)

        \# lslv indb0  (to check the number of copies, the number 
                of LPs, and the number of PPs.  In this case, 
                copies * LPs should equal PPs)

        The customer's "Copies" field was 1, yet LPs was 496 and
        PPs was 992.

        \# synclvodm -v cmgvg indb0
        The LV came back as "Updated", but "lslv indb0" indicated
        that there was no change.

        \# getlvcb -AT indb0 (to look at the LVCB)
        The LVCB was corrupt.  There was no "AIX LVCB" line at the
        top, and none of the fields had values.

        This is a problem with many third-party database products
        that use raw logical volumes.  AIX reserves the first 512
        bytes for the Logical Volume Control Block; if this information
        is overwritten by the database, then most of the information
        regarding the structure of the logical volume is corrupt.
        The primary result of this is the inability to make changes
        to the structure of the LV (i.e. further mirroring changes,
        increasing the size, etc.).  Sysback will continue to work
        around this problem, but other LVM commands will fail.

        The solution is to set the database to write AFTER the first
        512 bytes.  In this case, the LV must be backed up, recreated,
        and then set to skip the first 512 bytes.

        The customer also has these Sysback errors on a system running
        Sybase raw logical volumes.  Here is Sybase's solution:

 disk init
 name="\",
 physname="\",
 vdevno=\,
 size=\,
 vstart=1

The customer can either just ignore the error message and the
sysback backup will complete ok and will be able to correctly 
restore the system, but the user will not be able to increase
or add anymore mirroring to this lv

Next:   Close.



Support Line: Sysback error with raw LVs missing LVCBs ITEM: S5984L

Dated: March 1995 Category: N/A

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