Had a power outage, when turning back on the raid was missing..
Ran through the post suggested, managed to get back 4 of the 5 disks
mdadm --stop /dev/md0
mdadm --assemble --force --verbose /dev/md0 /dev/sd[abce]
root@OMVStore:~# mdadm --detail --scan --verbose
ARRAY /dev/md0 level=raid5 num-devices=5 metadata=1.2 name=OMVStore.local:Pool UUID=2e78b60b:c6be877d:728ea7fd:ce696755
root@OMVStore:~# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
md0 : active raid5 sdb sdc sdd sdf
11720536064 blocks super 1.2 level 5, 512k chunk, algorithm 2 [5/4] [_UUUU]
bitmap: 13/22 pages [52KB], 65536KB chunk
unused devices: <none>
RAID is back in the GUI however in degraded state, probably due to the missing drive /dev/sda drive, its there and SMART says all good.
tried the recover option and picking the drive, this yields a error message.
Also tried this from another post similar where it was missing a drive
mdadm --readwrite /dev/md0
mdadm: failed to set writable for /dev/md0: Device or resource busy
Any suggestions to get that drive attached and remove the degraded state of the RAID?