rpi5:~# mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Sun Aug 10 19:13:14 2025
        Raid Level : raid5
        Array Size : 15627544576 (14.55 TiB 16.00 TB)
     Used Dev Size : 3906886144 (3.64 TiB 4.00 TB)
      Raid Devices : 5
     Total Devices : 4
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Thu Jun 25 17:08:05 2026
             State : clean, degraded
    Active Devices : 4
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 0

            Layout : left-symmetric
        Chunk Size : 512K

Consistency Policy : bitmap

              Name : rpi5:0  (local to host rpi5)
              UUID : de8f9a7f:cc5ac2f5:9b57796e:5fd178cf
            Events : 30495

    Number   Major   Minor   RaidDevice State
       -       0        0        0      removed
       1       8       16        1      active sync   /dev/sdb
       2       8       32        2      active sync   /dev/sdc
       3       8       48        3      active sync   /dev/sdd
       5       8       64        4      active sync   /dev/sde
rpi5:~# ls /dev/sd*
/dev/sda  /dev/sdb  /dev/sdc  /dev/sdd  /dev/sde
rpi5:~# mdadm --zero-superblock /dev/sda
rpi5:~# mdadm /dev/md0 --add /dev/sda
mdadm: added /dev/sda
rpi5:~# mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Sun Aug 10 19:13:14 2025
        Raid Level : raid5
        Array Size : 15627544576 (14.55 TiB 16.00 TB)
     Used Dev Size : 3906886144 (3.64 TiB 4.00 TB)
      Raid Devices : 5
     Total Devices : 5
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Thu Jun 25 17:17:34 2026
             State : clean, degraded, recovering
    Active Devices : 4
   Working Devices : 5
    Failed Devices : 0
     Spare Devices : 1

            Layout : left-symmetric
        Chunk Size : 512K

Consistency Policy : bitmap

    Rebuild Status : 0% complete

              Name : rpi5:0  (local to host rpi5)
              UUID : de8f9a7f:cc5ac2f5:9b57796e:5fd178cf
            Events : 30497

    Number   Major   Minor   RaidDevice State
       6       8        0        0      spare rebuilding   /dev/sda
       1       8       16        1      active sync   /dev/sdb
       2       8       32        2      active sync   /dev/sdc
       3       8       48        3      active sync   /dev/sdd
       5       8       64        4      active sync   /dev/sde