[Fwd: Strange RAID-5 rebuild problem]

I am forwarding this from LKML, seems more appropriate here

-------- Original Message --------
Subject: Strange RAID-5 rebuild problem
Date: Sat, 1 Mar 2008 21:57:55 +0100
From: Michael Guntsche <[email protected]>
To: [email protected]
Newsgroups: gmane.linux.kernel

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

Bill Davidsen <[email protected]>
  "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot