Associate VGID with Volume Group Name

[Richard Ross]

For curiosity's sake,If I retrieve the vgid directly from a disk, is there any way to find out the Volume Group name that's assocated with the vgid? Yes .. I know about vgexport -s to create a map that includes the vgid, but was wandering if there was another way.

For example,

vgid=283173133ec80dbe = vg00

Thanks

[Jean-Louis Phelix]

No way ... You can even change the vgid using vgchgid command without changing lvmtab or special files. During activation, the only check done on disks is that all PV in a vg have the same vgid, that all ...

Regards.

[Bruno Vidal]

Hi,
Yes it is possible, this information vgid <-> VG is kept in /etc/lvmtab. But it is not really easy to retrieve it:
For example:
#echo "0x40C?2X" | adb /tmp/lvmtab
40C: 2096147D 3AB1ED17
You have the vgid just before the first disk of the vg. You have to write a small c programm to do that. The last solution is to directly retrieve the vgid on the device itself, it is always at the same place:
#echo "0x0002010?2X" | adb /dev/dsk/c8t2d0
2010: 2096147D 3AB1ED17

Good luck

[James R. Ferguson]

Hi Richard:

To add to the information already provided, remember that the very way to rename a volume group is to first 'vgexport' it [which removes the '/dev/vgXX' structures from the server and purges '/etc/lvmtab' of the VG information]. Having done this, you create a new directory representing the new VG name (e.g. /dev/myvg) and a group file with a unique minor number of your choice, and 'vgimport' the appropriate physical disk [either by matching the VGID or by specifying the actual physical disks].

Thus, the *name* of a volume group is "known" only through the device directory structure, and is not recorded on the physical disk(s) comprising the volume group.

Regards!

...JRF...

[Jean-Louis Phelix · Accepted solution]

Hi,

I'm very sorry but Bruno (who is 2 meters away from me ...) is perfectly rigth. vgchgid must be done BEFORE importing a vg. One of my colleagues wrote a long time ago a tool to read the lvmtab file. I give you a simplified version which is more beautiful than 'strings /etc/lvmtab and also give you the required vgid.

Regards.

[Dietmar Konermann]

... and in the case you need something "handy":

strings -t d /etc/lvmtab |
grep /dev |
grep -v /dev/dsk |
while read offset path; do
xd -An -j$(($offset+1024)) -N8 -tuL /etc/lvmtab |
read vgid1 vgid2
echo $path $vgid1-$vgid2
done

Best regards...
Dietmar.

[malay boy]

sorry for being sooo naive.what's the use of knowing the vgid?.Any specific used for vgid.

regards
mB

[Dietmar Konermann]

Imagine, you have a disk and need to know, if it's part of an configured volume group.

You look at the disk to get the VGID, e.g.:

# echo "0d8208?UU" | adb /dev/dsk/c11t0d0
2010: 3216063718 1046873340


Then you look at the VGID of the lvmtab, e.g. using the script above:


/dev/vg00 3216063718-1052129048
/dev/vgtobi 3216063718-1008239346
/dev/vgignite 3216063718-1006159972
/dev/vgoracle 3216063718-1012832752
/dev/vg03 3216063718-1052471874
/dev/vgmichael 3216063718-1053943064
/dev/vgheiko 3216063718-1046873340

And now you know that the disk is part of /dev/vgheiko. This is especially useful in a SAN, where lots of systems potentially use the disk.

BTW, here is another way to look at the VGID:

# echo "0d8208?UY" | adb /dev/dsk/c11t0d0
2010: 3216063718 2003 Mar 5 15:09:00

# uname -i
3216063718

You see that the vgcreate was issued on Mar 5 from this system.

Same applies for the PVID, which corresponds to the pvcreate timestamp.

# echo "0d8200?UY" | adb /dev/dsk/c11t0d0
2008: 3216063718 2002 Mar 11 14:36:31


Best regards...
Dietmar.

[Richard Ross]

Guys,

Thanks for all the responses. Dietmar's conclusion on why this is useful was right on mark and the script that Jean-Louis supplied makes this an easy task. Good info to have, just incase HP/UX renames the instances of the disk and you need to know which (if any) volume group that disk belonged to.

Thanks again

[Richard Ross]

Jean-Louis

I'm receiving the following when trying to compile the c program you supplied:

cc: "lvmtab.c", line 103: warning 527: Integral value implicitly converted to pointer in assignment.

cc: "lvmtab.c", line 103: warning 563: Argument #1 is not the correct type.

Can you help?

Thanks