linux-kernel - Strange RAID-5 rebuild problem

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Date:	Sat, 1 Mar 2008 21:57:55 +0100
From:	Michael Guntsche <mike@...loops.com>
To:	linux-kernel@...r.kernel.org
Subject: Strange RAID-5 rebuild problem

Ok, after going through benchmarking for the last few days, I now  
started acutally deploying the system.

I created a RAID-5 with a 1.0 superblock and let the RAID resync.
I had to reboot the computer for another update and did not think  
about thw rebuilding process since it should continue just fine after  
a restart. After a reboot I noticed that the RAID was in the  
following state.

/dev/md1:
         Version : 01.00.03
   Creation Time : Sat Mar  1 21:42:18 2008
      Raid Level : raid5
      Array Size : 1464982272 (1397.12 GiB 1500.14 GB)
   Used Dev Size : 976654848 (465.71 GiB 500.05 GB)
    Raid Devices : 4
   Total Devices : 4
Preferred Minor : 1
     Persistence : Superblock is persistent

     Update Time : Sat Mar  1 21:50:19 2008
           State : clean, degraded
  Active Devices : 3
Working Devices : 4
  Failed Devices : 0
   Spare Devices : 1

          Layout : left-symmetric
      Chunk Size : 256K

            Name : gibson:1  (local to host gibson)
            UUID : 80b0698e:d7c76d22:e231f03e:d25feba2
          Events : 32

     Number   Major   Minor   RaidDevice State
        0       8        2        0      active sync   /dev/sda2
        1       8       18        1      active sync   /dev/sdb2
        2       8       34        2      active sync   /dev/sdc2
        4       8       50        3      spare rebuilding   /dev/sdd2

mdadm -E /dev/sdd2:

/dev/sdd2:
           Magic : a92b4efc
         Version : 1.0
     Feature Map : 0x2
      Array UUID : 80b0698e:d7c76d22:e231f03e:d25feba2
            Name : gibson:1  (local to host gibson)
   Creation Time : Sat Mar  1 21:42:18 2008
      Raid Level : raid5
    Raid Devices : 4

  Avail Dev Size : 976655336 (465.71 GiB 500.05 GB)
      Array Size : 2929964544 (1397.12 GiB 1500.14 GB)
   Used Dev Size : 976654848 (465.71 GiB 500.05 GB)
    Super Offset : 976655592 sectors
Recovery Offset : 973312 sectors
           State : clean
     Device UUID : 5d6d28dd:c1d4d59d:3617c511:267c47f6

     Update Time : Sat Mar  1 21:55:44 2008
        Checksum : a1ca2174 - correct
          Events : 52

          Layout : left-symmetric
      Chunk Size : 256K

     Array Slot : 4 (0, 1, 2, failed, 3)
    Array State : uuuU 1 failed

/proc/mdstat showed now progress bar though. Ok, since he seems stuck  
I thought, why not just mark sdd2 as failed.
I was able to mark it as failed but looking at the detail again I saw  
"spare rebuilding" and I could not remove it.
Next I tried a fail/remove which also did not work. I stopped the  
array started it again, and THEN it removed the disk.
I tried this several times, the same result every time.

Just for kicks I created the RAID with a 0.90 superblock and tried  
the same thing. Lo and behold after stopping the array and starting  
it again the progress bar showed up and everything started rebuilding  
where it stopped earlier.

Is this "normal" or is this a superblock 1.0 related problem?

Current kernel is 2.6.24.2, mdadm is v2.6.4 from debian unstable.

I do not need the RAID right now so I could run some tests on it if  
someone wants me too.

Kind regards,
Michael
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