16.20. Replacing a failed disk in RAID

Procedure

1. Check the failed disk:

   1. View the kernel logs:

      # journalctl -k -f

   2. Search for a message similar to the following:

      md/raid:md0: Disk failure on sdd, disabling device.
      
      md/raid:md0: Operation continuing on 3 devices.

   3. Press Ctrl+C on your keyboard to exit the journalctl program.

2. Mark the failed disk as faulty:

   # mdadm --manage /dev/md0 --fail /dev/sdd

3. Optional: Check if the failed disk was marked correctly:

   # mdadm --detail /dev/md0

   At the end of the output is a list of disks in the /dev/md0 RAID where the disk /dev/sdd has the faulty status:

   Number   Major   Minor   RaidDevice State
      0       8       16        0      active sync   /dev/sdb
      1       8       32        1      active sync   /dev/sdc
      -       0        0        2      removed
      3       8       64        3      active sync   /dev/sde
   
      2       8       48        -      faulty   /dev/sdd

4. Remove the failed disk from the RAID:

   # mdadm --manage /dev/md0 --remove /dev/sdd

   警告

   If your RAID cannot withstand another disk failure, do not remove any disk until the new disk has the active sync status. You can monitor the progress using the watch cat /proc/mdstat command.

5. Add the new disk to the RAID:

   # mdadm --manage /dev/md0 --add /dev/sdf

   The /dev/md0 RAID now includes the new disk /dev/sdf and the mdadm service will automatically starts copying data to it from other disks.