Re: Help with recovering resized raid where machine crashed while PENDING

[Neil Brown]

Bug I expect... though actually it might be a different one to what
I was thinking.

Good to hear that this was not the way it was supposed to work.  The
failing RAID really had me worried that my files were lost. :)

Try to assemble the array normally with --verbose.
i.e.

  mdadm --assemble /dev/md3 --verbose /dev/sd[abcde]2
(or whatever the right list of devices is).

If this fails with something like

   mdadm: too-old timestamp on backup-metadata on ....

This is the message I saw:

meta:/dev# mdadm --assemble --verbose /dev/md3 sdb2 sdg2 sdh2 sdc2 sdf2
mdadm: looking for devices for /dev/md3
mdadm: sdb2 is identified as a member of /dev/md3, slot 0.
mdadm: sdg2 is identified as a member of /dev/md3, slot 4.
mdadm: sdh2 is identified as a member of /dev/md3, slot 3.
mdadm: sdc2 is identified as a member of /dev/md3, slot 1.
mdadm: sdf2 is identified as a member of /dev/md3, slot 2.
mdadm:/dev/md3 has an active reshape - checking if critical section needs to be restored
mdadm: too-old timestamp on backup-metadata on device-3
mdadm: too-old timestamp on backup-metadata on device-4
mdadm: Failed to find backup of critical section
mdadm: Failed to restore critical section for reshape, sorry.
      Possibly you needed to specify the --backup-file
meta:/dev# 

then you can assemble the array by 

   export MDADM_GROW_ALLOW_OLD=1
   mdadm --assemble ....(same command as above).

This requires mdadm-3.1.2 or newer.

And this worked great!

meta:/dev# MDADM_GROW_ALLOW_OLD=1 mdadm --assemble --verbose /dev/md3 sdb2 sdg2 sdh2 sdc2 sdf2
mdadm: looking for devices for /dev/md3
mdadm: sdb2 is identified as a member of /dev/md3, slot 0.
mdadm: sdg2 is identified as a member of /dev/md3, slot 4.
mdadm: sdh2 is identified as a member of /dev/md3, slot 3.
mdadm: sdc2 is identified as a member of /dev/md3, slot 1.
mdadm: sdf2 is identified as a member of /dev/md3, slot 2.
mdadm:/dev/md3 has an active reshape - checking if critical section needs to be restored
mdadm: accepting backup with timestamp 1308555399 for array with timestamp 1309424388
mdadm: restoring critical section
mdadm: added sdc2 to /dev/md3 as 1
mdadm: added sdf2 to /dev/md3 as 2
mdadm: added sdh2 to /dev/md3 as 3
mdadm: added sdg2 to /dev/md3 as 4
mdadm: added sdb2 to /dev/md3 as 0
mdadm: /dev/md3 has been started with 5 drives.
meta:/dev# 

Happy hacking,
-- 
Petter Reinholdtsen