All disks shown as spares (S):
rpi5:~# cat /proc/mdstat
Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : inactive sdd[3](S) sda[0](S) sdc[2](S) sdb[1](S) sde[5](S)
19534432440 blocks super 1.2
Try reassembling the array
mdadm -A /dev/md0
If you now have a “removed” state for one of the disks, you can readd it again, just make sure you zero-out the superblock on the correct drive:
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