Re: trouble repairing raid10

On 06/03/2010 02:19 AM, Neil Brown wrote:

On Wed, 02 Jun 2010 18:25:58 +0200
Nicolas Jungers[off-list ref]  wrote:

quoted

I've a 4 HD raid10 with to failed drive.  Any attempt I made to add 2
replacement disks fail consistently.

mdadm -Af /dev/md1 /dev/sdm2 /dev/sdp2   /dev/sdb2  /dev/sdd2
mdadm: failed to add /dev/sdd2 to /dev/md1: Device or resource busy

Any idea why sdd2 is busy??

No, because sdd2 is not busy.  I have 4 spares (b, c, d and e), the one 
I set in fourth position in the above mdadm -Af command is reported as 
busy, whatever the one I set there.  The same disk in third position get 
a mdadm superblock write on them.  I suspect then an incorrect error 
message.

quoted

mdadm: /dev/md1 assembled from 2 drives and 1 spare - not enough to
start the array.

or

root@disk:~# mdadm -AR /dev/md1 /dev/sdm2 /dev/sdp2
mdadm: failed to RUN_ARRAY /dev/md1: Input/output error
mdadm: Not enough devices to start the array.
root@disk:~# mdadm --add /dev/md1 /dev/sdb2
mdadm: add new device failed for /dev/sdb2 as 4: Invalid argument


The array is in near mode and I lost disk 0 and 1.  Does it mean that my
data are toasted?

Yes.  RAID10 can survive the failure of 2 non-adjacent devices and sometimes
2 adjacent devices.  But not 0 and 1 of a near=2 array.

So if those devices are really dead, so is your data.

If one of these is actually usable and just had a transient failure then you
could try re-creating the array with the drives, or 'missing' in the right
order and with the write layout/chunksize set.
You would need to be user the 'Data Offset' was the same, which unfortunately
can require using exactly the same version of mdadm as created the array in
the first place.

will try that, it was created on a beta of Ubuntu 10.04 and is now 
running on shipped 10.04 (kernel 2.6.32)

NeilBrown

quoted

mdadm --examine /dev/sdm2
/dev/sdm2:
            Magic : a92b4efc
          Version : 1.2
      Feature Map : 0x0
       Array UUID : d90ad6fe:1355134f:f83ffadc:a4fe7859
             Name : m1:1
    Creation Time : Thu Apr  1 21:28:58 2010
       Raid Level : raid10
     Raid Devices : 4

   Avail Dev Size : 3907026909 (1863.02 GiB 2000.40 GB)
       Array Size : 7814049792 (3726.03 GiB 4000.79 GB)
    Used Dev Size : 3907024896 (1863.01 GiB 2000.40 GB)
      Data Offset : 272 sectors
     Super Offset : 8 sectors
            State : clean
      Device UUID : e217355e:632ac2f0:8120e55e:3878bd88

      Update Time : Wed Jun  2 12:31:39 2010
         Checksum : feef2809 - correct
           Events : 1377156

           Layout : near=2, far=1
       Chunk Size : 1024K

      Array Slot : 3 (failed, failed, 2, 3)
     Array State : __uU 2 failed
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