1. mdadm -Ss
2. mdadm -CR /dev/md0 -l0 -n 2 /dev/loop[01]
   mdadm: /dev/loop0 appears to be part of a raid array:
   level=raid5 devices=3 ctime=Wed Nov 12 13:07:49 2025
   mdadm: /dev/loop1 appears to be part of a raid array:
   level=raid5 devices=3 ctime=Wed Nov 12 13:07:49 2025
   mdadm: Defaulting to version 1.2 metadata
   mdadm: array /dev/md0 started.

1. mdadm -D /dev/md0
   /dev/md0:
   Version : 1.2
   Creation Time : Wed Nov 12 15:09:43 2025
   Raid Level : raid0
   Array Size : 405504 (396.00 MiB 415.24 MB)
   Raid Devices : 2
   Total Devices : 2
   Persistence : Superblock is persistent

Update Time : Wed Nov 12 15:09:43 2025
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Layout : original
Chunk Size : 512K

Consistency Policy : none

Name : nigel.usersys.redhat.com:0 (local to host nigel.usersys.redhat.com)
UUID : 58ed5337:f67c9c59:1c033cbe:f895fccd
Events : 0

Number Major Minor RaidDevice State
0 7 0 0 active sync missing
1 7 1 1 active sync missing

1. mdadm --grow /dev/md0 --level=5 --add /dev/loop2
   mdadm: level of /dev/md0 changed to raid5
   mdadm: added /dev/loop2
   mdadm: /dev/md0: cannot open component unknown
   mdadm: failed to write 'raid0' to '/sys/block/md0/md//level' (Invalid argument)

1. rpm -qa |grep mdadm
   mdadm-4.3-3.el9.x86_64

1. mdadm -V
   mdadm - v4.4 - 2025-05-01