Question about number in mdadm --detail and /proc/mdstat when replacing drive

ergosteur · 03-06-2017, 09:33 PM

Just rebooted my Debian server without properly checking that all the drives were properly connected...

Anyway, I'm running a raid5 with mdraid, so the drive is now showing as "removed" -

Code:

# mdadm --detail --scan /dev/md0
/dev/md0:
        Version : 1.2
  Creation Time : Mon Feb 20 15:30:24 2017
     Raid Level : raid5
     Array Size : 15627548672 (14903.59 GiB 16002.61 GB)
  Used Dev Size : 3906887168 (3725.90 GiB 4000.65 GB)
   Raid Devices : 5
  Total Devices : 4
    Persistence : Superblock is persistent

    Update Time : Mon Mar  6 22:18:44 2017
          State : clean, degraded 
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : ana-nas:0  (local to host ana-nas)
           UUID : 1c96f3e6:d996243e:91fa4af1:636f787f
         Events : 5672

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd
       3       8       64        3      active sync   /dev/sde
       4       0        0        4      removed
# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] 
md0 : active raid5 sdb[0] sde[3] sdd[2] sdc[1]
      15627548672 blocks super 1.2 level 5, 512k chunk, algorithm 2 [5/4] [UUUU_]
      
unused devices: <none>

I reconnected the drive and re-added it

Code:

# mdadm --add /dev/md0 /dev/sdf
mdadm: added /dev/sdf

But now the drive shows as device number 5 instead of 4. Is this the intended behaviour? Is there any way to get /dev/sdf to show as device 4 again to satisfy my OCD?

Code:

# mdadm --detail --scan /dev/md0
/dev/md0:
        Version : 1.2
  Creation Time : Mon Feb 20 15:30:24 2017
     Raid Level : raid5
     Array Size : 15627548672 (14903.59 GiB 16002.61 GB)
  Used Dev Size : 3906887168 (3725.90 GiB 4000.65 GB)
   Raid Devices : 5
  Total Devices : 5
    Persistence : Superblock is persistent

    Update Time : Mon Mar  6 22:29:03 2017
          State : clean, degraded, recovering 
 Active Devices : 4
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 1

         Layout : left-symmetric
     Chunk Size : 512K

 Rebuild Status : 0% complete

           Name : ana-nas:0  (local to host ana-nas)
           UUID : 1c96f3e6:d996243e:91fa4af1:636f787f
         Events : 5972

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd
       3       8       64        3      active sync   /dev/sde
       5       8       80        4      spare rebuilding   /dev/sdf
# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] 
md0 : active raid5 sdf[5] sdb[0] sde[3] sdd[2] sdc[1]
      15627548672 blocks super 1.2 level 5, 512k chunk, algorithm 2 [5/4] [UUUU_]
      [>....................]  recovery =  0.0% (2420676/3906887168) finish=456.9min speed=142392K/sec