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I have a raid5 set up with mdadm and had to replace one broken hard drive. It worked for a while, but for some reason, became inactive after a couple of weeks.

I'm pretty sure that the missing drive /dev/sdb is also the one I replaced:

# sudo mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
        Raid Level : raid0
     Total Devices : 3
       Persistence : Superblock is persistent

         State : inactive



Working Devices : 3


          Name : REMOTENAME:0  (local to host REMOTENAME)
          UUID : 59f98bf3:274707c2:2d79bc60:f0217294
        Events : 212054

Number   Major   Minor   RaidDevice

   -       8       64        -        /dev/sde
   -       8       32        -        /dev/sdc
   -       8       48        -        /dev/sdd

Next, /proc/mdstat contains:

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : inactive sdc[1](S) sde[4](S) sdd[2](S)
      23441683464 blocks super 1.2

unused devices: <none>

The hard drive state seems to be ok, as no errors are with smartctl for /dev/sdb.

Lastly, mdadm --examine /dev/sdb yields:

/dev/sdb:
   MBR Magic : aa55
Partition[0] :   4294967295 sectors at            1 (type ee)

EDIT: Thank you all for your comments! I'm actually not the one who setup that RAID, more like the lucky one inheriting the responsibility for it. I'll gladly take your advicde for the next setup :)

You're actually right, that it says raid0 now. I found a textfile where I saved the output of mdadm --detail /dev/md0 which might be insightful?

# sudo mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Tue Jul 24 13:22:48 2018
        Raid Level : raid5
        Array Size : 23441682432 (22355.73 GiB 24004.28 GB)
     Used Dev Size : 7813894144 (7451.91 GiB 8001.43 GB)
      Raid Devices : 4
     Total Devices : 4
       Persistence : Superblock is persistent
     Intent Bitmap : Internal
       Update Time : Mon Sep  4 07:36:57 2023
             State : clean, checking
    Active Devices : 4
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 0
            Layout : left-symmetric
        Chunk Size : 512K
Consistency Policy : bitmap
      Check Status : 77% complete
              Name : REMOTENAME:0  (local to host REMOTENAME)
              UUID : 59f98bf3:274707c2:2d79bc60:f0217294
            Events : 212051
    Number   Major   Minor   RaidDevice State
       5       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd
       4       8       64        3      active sync   /dev/sde

Possibly related, I found some differences between the hard drive /dev/sdb and the other ones of the raid:

# sudo lshw -class disk
...
  *-disk
       description: ATA Disk
       product: WDC WD80EFZZ-68B
       vendor: Western Digital
       physical id: 0.0.0
       bus info: scsi@1:0.0.0
       logical name: /dev/sdb
       version: 0A81
       serial: ---
       size: 7452GiB (8001GB)
       capabilities: gpt-1.00 partitioned partitioned:gpt
       configuration: ansiversion=5 guid=a931e3f0-c80c-447b-b4f6-e3a06b9b51a7 logicalsectorsize=512 sectorsize=4096
  *-disk
       description: ATA Disk
       product: WDC WD80EFZX-68U
       vendor: Western Digital
       physical id: 0.0.0
       bus info: scsi@2:0.0.0
       logical name: /dev/sdc
       version: 0A83
       serial: ---
       size: 7452GiB (8001GB)
       configuration: ansiversion=5 logicalsectorsize=512 sectorsize=4096
...

Previously, there was no partitioned info given on the old drive /dev/sdb:

  *-disk
       description: ATA Disk
       product: WDC WD80EFZX-68U
       vendor: Western Digital
       physical id: 0.0.0
       bus info: scsi@1:0.0.0
       logical name: /dev/sdb
       version: 0A83
       serial: ---
       size: 7452GiB (8001GB)
       configuration: ansiversion=5 logicalsectorsize=512 sectorsize=4096

EDIT2:

As the array was inactive, I reactivated it successfully using sudo mdadm --run /dev/md0. You are right, that somehow, potentially after a reboot, /dev/sdb dropped out of the array/was removed?...

# sudo mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Tue Jul 24 13:22:48 2018
        Raid Level : raid5
        Array Size : 23441682432 (22355.73 GiB 24004.28 GB)
     Used Dev Size : 7813894144 (7451.91 GiB 8001.43 GB)
      Raid Devices : 4
     Total Devices : 3
       Persistence : Superblock is persistent

 Intent Bitmap : Internal

   Update Time : Thu Nov  2 14:10:31 2023
         State : clean, degraded 
Active Devices : 3



Working Devices : 3
    Failed Devices : 0
     Spare Devices : 0


        Layout : left-symmetric
    Chunk Size : 512K




Consistency Policy : bitmap


          Name : REMOTENAME:0  (local to host REMOTENAME)
          UUID : 59f98bf3:274707c2:2d79bc60:f0217294
        Events : 212077

Number   Major   Minor   RaidDevice State
   -       0        0        0      removed
   1       8       32        1      active sync   /dev/sdc
   2       8       48        2      active sync   /dev/sdd
   4       8       64        3      active sync   /dev/sde

My question now would be: Should I re-format the disk on /dev/sdb before adding it to the array again?

And a bonus question, as it has been pointed out: Can you savely transform an existing raid5 into, e.g. raid1 or raid6?

lupus83
  • 11

0 Answers0