I recently had a very bad experience with OpenMediaVault. I had created a Raid 0 (so 2 disks mirrored). It all was working fine until recently I had a power issue. The raid was missing and in the past I tried to recreate the RAID but to my surprise disks were missing.
I said before doing anything let me move it to a windows box and try to copy all the data. I did found some tools (expensive) that could fix the issue or recover the data. I did not wanted to throw my money away so I tried with 1 disk to fix it on the Unix level. Nothing worked but when I did ran this command the raid was available but degraded.
mdadm --assemble --scan
Result:
mdadm: /dev/md0 has been started with 1 drive (out of 2).
After this I could initialise the other disk and add again the disk to the RAID volume. I just wanted to share my experience and maybe it helps someone that is very worried and if it works for you great !
Show status of Raid
mdadm -D /dev/md0
Raid seems to be inactive ?
Start the raid by doing this command
mdadm --run /dev/md0
add a disk to the raid
mdadm --manage /dev/md0 --add /dev/sdb
Grow Size of raid to use up all space
mdadm --grow /dev/md0 --size max
Remove other drives no longer visible?
Well just reduce the raid to the active disks
mdadm --grow /dev/md0 --raid-devices=2
Monitor Raid status
watch cat /proc/mdstat
Monitor Disk activity
watch iostat -k 1 2
apt-get -y install nvme-cli