[SLL] get md RAID array to rebuild even if read errors?

[Jeremy C. Reed]

Any ideas on how to get mdadm or md to rebuild even if read errors?

We had a failed disk. We replaced it and did:

  /sbin/mdadm --fail /dev/md0 /dev/sdb2
  /sbin/mdadm --remove /dev/md0 /dev/sdb2
  /sbin/mdadm --zero-superblock /dev/sdc2
  /sbin/mdadm --add /dev/md0 /dev/sdc2

# cat /proc/mdstat 
Personalities : [raid1] 
md0 : active raid1 sdc2[2] sda2[0]
      71577536 blocks [2/1] [U_]
      [>....................]  recovery =  0.9% (691072/71577536) 
finish=148.6min speed=7944K/sec
unused devices: <none>


But it fails repeatedly (over 350 times by now) at:

Feb 14 12:36:25 foo kernel: scsi0: ERROR on channel 0, id 0, lun 0, CDB: 
Read (10) 00 00 50 ec cd 00 00 80 00 
Feb 14 12:36:25 foo kernel: Info fld=0x50ece5, Current sda: sense key 
Medium Error
Feb 14 12:36:25 foo kernel: Additional sense: Unrecovered read error
Feb 14 12:36:25 foo kernel: end_request: I/O error, dev sda, sector 
5303501
Feb 14 12:36:25 foo kernel: raid1: sda: unrecoverable I/O read error for 
block 5094656
Feb 14 12:36:25 foo kernel: md: md0: sync done.

(Then it starts again ... kernel: md: syncing RAID array md0 and so on 
...)

Bad luck. Two disks bad. And now can't rebuild the newly added disk 
(sdc2).

Any way to force it to continue with the syncing even if a "read error"?

badblocks doesn't even see that bad block.

If you have suggestions on getting SMART to mark it bad.

Also I can't use debugfs with icheck to see the inode number because says 
"icheck: Filesystem not open". Any ideas? If I could find the inode 
number, then maybe I could rewrite that area and SMART will mark it as 
bad.

  Jeremy C. Reed