Sysback error with raw LVs missing LVCBs
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
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:
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
Support Line: Sysback error with raw LVs missing LVCBs ITEM: S5984L
Dated: March 1995 Category: N/A
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