Superblock problems when creating a RAID array

From: Adam Nielsen (a.nielsen_at_optushome.com.rem.ove.au)
Date: 05/30/04 

Date: Sun, 30 May 2004 14:45:52 +1000

Hi,

I'm trying to create a RAID5 array from four hard drives, but one drive
seems really doesn't want to become part of the array. To me it looks
like there is a problem with the drive, but all the tests I have run
seem to indicate the drive is working perfectly.

$ mkraid /dev/md0
handling MD device /dev/md0
analyzing super-block
disk 0: /dev/sdd1, 17718256kB, raid superblock at 17718144kB
disk 1: /dev/sdb1, 17718256kB, raid superblock at 17718144kB
disk 2: /dev/sdc1, 17718256kB, raid superblock at 17718144kB
disk 3: /dev/sde1, 17718256kB, raid superblock at 17718144kB

$ lsraid -d /dev/sdb1
lsraid: Device "/dev/sdb1" does not have a valid raid superblock

$ lsraid -d /dev/sdc1
lsraid: Device "/dev/sdb1" does not have a valid raid superblock
lsraid: Device "/dev/sdb1" does not have a valid raid superblock
lsraid: Device "/dev/sdb1" does not have a valid raid superblock
lsraid: Device "/dev/sdb1" does not have a valid raid superblock
[dev 9, 0] /dev/md0 F79BC9E7.81937715.D50F957C.48C9BA14 online
[dev 8, 49] /dev/sdd1 F79BC9E7.81937715.D50F957C.48C9BA14 good
[dev ?, ?] (unknown) 00000000.00000000.00000000.00000000 missing
[dev 8, 33] /dev/sdc1 F79BC9E7.81937715.D50F957C.48C9BA14 good
[dev 8, 65] /dev/sde1 F79BC9E7.81937715.D50F957C.48C9BA14 good

$ cat /etc/raidtab
raiddev /dev/md0
  raid-level 5
  nr-raid-disks 4
  nr-spare-disks 0
  persistent-superblock 1
  parity-algorithm left-symmetric
  chunk-size 128
  device /dev/sdd1
  raid-disk 0
  device /dev/sdb1
  raid-disk 1
  device /dev/sdc1
  raid-disk 2
  device /dev/sde1
  raid-disk 3

If I extract the RAID superblock with dd, it is almost identical to the
superblocks on the other drives so it looks like it's being written
correctly, and I know it's the right superblock, because if I blank it
out on the other drives:

$ dd if=/dev/zero of=/dev/sdc1 bs=1K skip=17718144 seek=17718144 count=1

Then that drive is no longer recognised as part of the RAID array.

I'm stumped as to what the problem is, so if anyone has any ideas...!

Thanks,
Adam.

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