To reappear
To reappear the raid when it simply disappear
# mdadm -S /dev/md0
# mdadm --assemble /dev/md0 /dev/sd[bcdef] --verbose --force
To Force
To force a check of the entire array while it’s online. On /dev/md0, run as root:
# echo check > /sys/block/md0/md/sync_action
To Check
To check raid status
# mdadm -D /dev/md0
And if you have a error like: Impossible to mount file system : Structure needs cleaning
more precisely:
Failed to execute command 'export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin; export LANG=C; mount -v --source '/dev/disk/by-id/md-name-openmediavault:raid9disks' 2>&1' with exit code '32': mount: mount /dev/md0 on /srv/dev-disk-by-id-md-name-openmediavault-raid9disks failed: Structure needs cleaning
You must do this:
# fsck /dev/md0
And, if needed, fix all errors. After that you can mount the file system.
If not try this:
# fsck.ext4 -f /dev/disk/by-id/md-name-openmediavault:raid9disks
# mount -a