very weird uuid problem with vol_id and /dev/disk/by-uuid/

Dolf Andringa dolf.andringa at
Wed Jun 3 19:41:34 UTC 2009

hey people.

I have a very weird problem in an Ubuntu Hardy machine running inside a 
Xen virtual machine.

I have /dev/sdb1 setup with LVM. After a reboot this didn't come back up 
and the problem seems to be related to a uuid problem (physical volume's 
uuid is wrong, causing lvm not to find the volume group).

Somehow "vol_id /dev/sdb" returns "47caf26c-7491-4b24-a5cc-cd7825518ef3" 
as the vol_id, but "vol_id /dev/sdb1" says "Unkown volume type". This is 
weird, since normally, only the partitions should return a vol_id, not 
the block device.
When  I run "fdisk -l" I do see the correct partition table though:

Disk /dev/sdb: 4294 MB, 4294967296 bytes
255 heads, 63 sectors/track, 522 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x58a3ad78

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1         522     4192933+  8e  Linux LVM

When I take a look at /dev/disk/by-uuid/ I see the following:
lrwxrwxrwx 1 root root 10 2009-06-03 21:21 
47caf26c-7491-4b24-a5cc-cd7825518ef3 -> ../../sdb1
lrwxrwxrwx 1 root root 10 2009-06-03 21:21 
64db3117-17d9-463f-b560-7df7392a5816 -> ../../sda1
lrwxrwxrwx 1 root root 10 2009-06-03 21:21 
c9e88347-58fd-4c8d-93d8-c0d8228d58eb -> ../../sda2

So there is a link to /dev/sdb1, and /dev/sdb1 seems to contain a uuid, 
but it is the same as what vol_id reports as the uuid for /dev/sdb. It 
really seams the mappings of the devices got mixed up, but I don't know 
how, and how to fix this.

I hope someone can help me out with this.



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