[clug] LVM recovery -- Canberra LUG a last resort!
Daniel Rose
drose at nla.gov.au
Sun Nov 4 08:27:59 GMT 2007
Mark Triggs wrote:
> Daniel Rose <drose at nla.gov.au> writes:
>
>> All I think I've altered on disk are these bytes near the beginning of
>> the partition.
>>
>> [...binary...]LABELONE [...binary...] LVM2
>> 0016oVVgdWIVKqB0yPXk2Acu5ZxcIgMj5JD [...binary...]
>>
>> By doing
>> pvcreate -u 6oVVgd-WIVK-qB0y-PXk2-Acu5-ZxcI-gMj5JD /dev/hdd2
>> Software RAID md superblock detected on /dev/hdd2. Wipe it? [y/n] n
>> Physical volume “/dev/hdd2″ successfully created
>>
>> As suggested by someone somewhere on the Internet.
>>
> [...]
>
>> So... I'm not sure what's going on. Further along the disk can be found
>> text files detailing the construction, first with seqno1, 2 and finally
>> this (edited) promise of potential success:
>>
>> main {
>>
> [...]
>
>
>> # Generated by LVM2: Tue Nov 21 18:40:21 2006
>>
>>
>> It seems to me that given this information, it should not be
>> particularly difficult to do this.
>>
>
>
> This article:
>
> http://www.linuxjournal.com/article/8874
>
> describes restoring the LVM metadata using the stored information from
> the beginning of the raw disk. A half-baked test with a USB device here
> seemed to work, but don't blame me if you lose your data ;o)
>
Well it doesn't work for me:
# cat /proc/mdstat
Personalities :
md1 : inactive hdd1[0]
104320 blocks
md2 : inactive hdd2[0]
78043648 blocks
# mdadm -A -s /dev/md2
mdadm: device /dev/md2 already active - cannot assemble it
And:
# vgcfgrestore -f main main
Couldn't find device with uuid '6oVVgd-WIVK-qB0y-PXk2-Acu5-ZxcI-gMj5JD'.
Couldn't find all physical volumes for volume group main.
Restore failed.
# sudo pvcreate -u 6oVVgd-WIVK-qB0y-PXk2-Acu5-ZxcI-gMj5JD /dev/hdd2
Can't open /dev/hdd2 exclusively. Mounted filesystem?
# vgcfgrestore -f main main
Restored volume group main
See how the pvcreate apparently failed, but now vgcfrestore is happy to
report a restored group?
# vgscan
Reading all physical volumes. This may take a while...
No volume groups found
unhappy. Hm...
pvscan and pvdisplay also come in empty-handed. I suspect that this is
abnormal behaviourr, however I seem to be getting closer!
# vgchange main -a y
device-mapper: reload ioctl failed: Invalid argument
device-mapper: reload ioctl failed: Invalid argument
2 logical volume(s) in volume group "main" now active
# lvscan
ACTIVE '/dev/main/root' [74.12 GB] inherit
ACTIVE '/dev/main/swap' [256.00 MB] inherit
# ls /dev/mapper/main-root
/dev/mapper/main-root
# mount /dev/mapper/main-root /wow
mount: /dev/mapper//main-root: can't read superblock
# cat /dev/mapper/main-root
#
So I've got the device node, but it's empty; and that's probably because
/proc/mdstat reports the partition(s) as inactive.
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