Determining which drive failed in RAID 5 array

[Daniel Buggie]

On Fri, 2005-08-05 at 10:54 -0700, Brian D. McGrew wrote:
> I've got a RAID 5 array with four drives in it.  One of them is failed,
> I look at /proc/mdstat and it shows me 4/3 [UUU_]. 
> 
>  
> 
> How do I know which one is faied???
> 
>  
> 

If you sent out the full output from that command that would have
helped.  However, a couple of things should tell you which one failed.

/proc/mdstat should list out all the partitions currently in the RAID on
the same line that identifies which device it is (md0, md1, etc.).  If
you know which devices should be there that should help.

For example (on a RAID 1):

# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda1[0]
      15880128 blocks [2/1] [U_]

I know that /dev/sdb1 was the other device, so I can work from there.

Also mdadm --detail /dev/md[x] should be able to tell you as well.

# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.01
  Creation Time : Tue Aug  2 01:30:19 2005
     Raid Level : raid1
     Array Size : 15880128 (15.14 GiB 16.26 GB)
    Device Size : 15880128 (15.14 GiB 16.26 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Tue Aug  2 06:27:21 2005
          State : clean, degraded
  Active Devices : 1
Working Devices : 1
  Failed Devices : 1
  Spare Devices : 0


    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       0        0       -1      removed
       2       8       17       -1      faulty   /dev/sdb1
           UUID : 44fbd581:ccf5eb3c:db517a25:9b319c57
         Events : 0.799


If you have rebooted though, this will probably all go out the window...
since what was /dev/sdb will probably now be /dev/sda, etc.