MD RAID supports Grow but not Shrink

Describe the bug

One of my RAID Mirror disks was dying so I replaced it. After an unrelated issue with thinking I could/should remove the drive offline, replace, reboot, and extend (md freaks out and refuses with a mdadm: add new device failed for /dev/sdd as 2: Invalid argument error until I put back in the old drive and grow the array into the new drive) I successfully extended the mirror to three disks, and removed the dying disk. However even after reboot the array says it's degraded because it's expecting three total disks (one being removed.) I solved this with mdadm --grow /dev/md0 --raid-devices=2 to shrink the array back down to 2 disks. This isn't apparently supported in the GUI however, complicating disaster recovery.

To Reproduce

Steps to reproduce the behavior:

1. Extend a 2-disk RAID Mirror array to 3 disks.
2. After rebuild, properly remove one of the original disks using the OMV GUI.
3. Note that despite no obvious issues, the array is listed in the GUI as degraded.
4. Note that to get a "clean" array, logging in via SSH and running something like mdadm --grow /dev/md0 --raid-devices=2 is required, outside the normal OMV GUI.

Expected behavior

All basic NAS operations, especially when recovering from failure/disaster, should be possible and intuitive from within OMV.

openmediavault Server (please complete the following information):

• OS version: Linux openmediavault 6.12.12+bpo-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.12-1~bpo12+1 (2025-02-23) x86_64 GNU/Linux
• openmediavault version: 7.7.4-1