LVM problem

[Dan Coutu]

I'm extending an LVM volume in the same way that I did on an almost 
identical machine last week. Have an existing RAID array setup on 
/dev/sda with /dev/sda1 setup as the boot partition and /dev/sda2 as a 
logical volume. Added new RAID drives that show up as /dev/sdb. They 
show up on boot, great! Do a pvcreate /dev/sdb and it reports that all 
is well. mkfs on /dev/sdb also goes well.

When I then tried vgextend the system seems confused. Here's the output:

# vgextend VolGroup00 /dev/sdb
  Couldn't find device with uuid 'oACqnk-YQTQ-IiGy-F6Pj-UoBB-kUqM-g6Yu3D'.
  Couldn't find all physical volumes for volume group VolGroup00.
  Couldn't find device with uuid 'oACqnk-YQTQ-IiGy-F6Pj-UoBB-kUqM-g6Yu3D'.
  Couldn't find all physical volumes for volume group VolGroup00.
  Volume group "VolGroup00" not found.

Eh? What's up with that? This did not happen on the other system. All 
went smoothly.

A little more investigation shows that pvdisplay, vgdisplay and 
lvdisplay all complain about not finding the device with that UUID value.

This is not happiness.

So of course I look on the Red Hat site because this is RHEL V4 and find 
that is says that the LVM metadata has been corrupted somehow. I assume 
that they're referring to the LVM metadata on /dev/sda2. They provide a 
procedure for recovering the metadata and it seems simple enough except 
for one detail, this note in a big red box with a stop sign in it.


    Caution

You should not attempt this procedure with a working LVM logical volume. 
You will lose your data if you specify the incorrect UUID.


Given that this is a production server that is currently in use I'm 
nervous. The RH instructions show how to find the correct UUID, which is 
not the UUID being asked for in the above error message. The part that 
worries me is that the example shows recovering the *same* UUID as is 
found in the error message where I'm not seeing the error message UUID 
in the /etc/lvm/archive/VolGroup00_*.vg files anywhere. So how can I be 
absolutely certain that I'm using the correct UUID? No way can I afford 
to nuke the whole system.

Thanks for any ideas/suggestions!

Dan