[linux-lvm] simple LVM disk failure recover

[benry <benry@autistici.org>]

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Hi,
I'm quite new to LVM and I think to have a quite simple problem, but I
can not find a clear answer to it and, since it is a quite critical
problem, I'm asking to you for the right solution before messing up
everything.

I have an LVM volume made by two raid sda and sdb, with an XFS
filesystem on it; sda had a failure and its data is completely lost...
what I would like to do is to restore at least what is contained in sdb.
(The situation displayed by "lvdisplay -mP" is reported at the end of
this mail).

I tried this command: "vgchange -P -a y raid", but the device
/dev/raid/data does not exist and the /dev/mapper/raid-data I used to
mount the volume seems to be not accessible:

# xfs_check /dev/mapper/raid-data
xfs_check: /dev/mapper/raid-data is invalid (cannot read first 512 bytes)

Is the data contained in sdb recoverable? (as far as I understood, it
should) And if it is the case, which should be the right procedure to
restore it?


Thanks in advance for your help.

Enrico

# lvdisplay -mP
  Partial mode. Incomplete volume groups will be activated read-only.
  /dev/sda: read failed after 0 of 4096 at 0: Input/output error
  /dev/sda: read failed after 0 of 4096 at 0: Input/output error
  /dev/sda: read failed after 0 of 4096 at 19989989883904: Input/output
error
  /dev/sda: read failed after 0 of 4096 at 19989989941248: Input/output
error
  /dev/sda: read failed after 0 of 4096 at 0: Input/output error
  /dev/sda: read failed after 0 of 4096 at 4096: Input/output error
  /dev/sda: read failed after 0 of 4096 at 0: Input/output error
  Couldn't find device with uuid 'AkLdC5-wPgi-hDbv-Sqf3-2wBv-hBzu-2OhDaQ'.
  /dev/sda: read failed after 0 of 4096 at 0: Input/output error
  /dev/sda: read failed after 0 of 4096 at 0: Input/output error
  Couldn't find device with uuid 'AkLdC5-wPgi-hDbv-Sqf3-2wBv-hBzu-2OhDaQ'.
  --- Logical volume ---
  LV Name                /dev/raid/data
  VG Name                raid
  LV UUID                4rjFt7-ZuQX-f3n4-iDVR-2gJv-5cFf-77gG5f
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                36.36 TB
  Current LE             9531968
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           254:0

  --- Segments ---
  Logical extent 0 to 4765983:
    Type                linear
    Physical volume     unknown device
    Physical extents    0 to 4765983

  Logical extent 4765984 to 9531967:
    Type                linear
    Physical volume     /dev/sdb1
    Physical extents    0 to 4765983
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