Re: Two degraded mirror segments recombined out of sync for massive data loss

[Bill Davidsen <davidsen@tmr.com>]

Phillip Susi wrote:
> The gist of the problem is this: after booting a mirror in degraded mode
> with only the first disk, then doing the same with only the second disk,
> then booting with both disks again, mdadm happily recombines the two
> disks out of sync, causing two divergent filesystems to become munged
> together.
>
> The problem was initially discovered testing the coming lucid release of
> Ubuntu doing clean installs in a virtualization environment, and I have
> reproduced it manually activating and deactivating the array built out
> of two lvm logical volumes under Karmic.  What seems to be happening is
> that when you activate in degraded mode ( mdadm --assemble --run ), the
> metadata on the first disk is changed to indicate that the second disk
> was faulty and removed.  When you activate with only the second disk,
> you would think it would say the first disk was faulty, removed, but for
> some reason it ends up only marking it as removed, but not faulty.  Now
> both disks are degraded.
>
> When mdadm --incrmental is run by udev on the first disk, it happily
> activates it since the array is degraded, but has one out of one active
> member present, with the second member faulty,removed.  When mdadm
> --incremental is run by udev on the second disk, it happily slips the
> disk into the active array, WITHOUT SYNCING.
>
> My two questions are:
>
> 1) When doing mdadm --assemble --run with only the second disk present,
> shouldn't it mark the first disk as faulty, removed instead of only removed?
>
> 2) When mdadm --incremental is run on the second disk, shouldn't it
> refuse to use it since the array says the second disk is faulty, removed?
>
> The bug report related to this can be found at:
>
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/557429
>
>   

Is any of this due to the rather elderly versions of the kernel and 
mdadm which Ubuntu was running?

-- 
Bill Davidsen <davidsen@tmr.com>
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein