My hardware setup is
7 - Check your RAID array: mdadm -D /dev/YOUSHOULDKNOW
8 - My array was running fine.
9 - Make a mountpoint in /mnt: mkdir /mnt/YOUSHOULDKNOW
10 - Mount array to mountpoint: mount /dev/YOUSHOULDKNOW /mnt/YOUSHOULDKNOW
11 - Move to backup directory on array
12 - Check your backup: fsarchiver archinfo backup.fsa
(Find out source partition, in my case the backup did not include the swap-partition, so I was pretty sure to backup just TO the first partition of my system disk)
13 - Find out what device name the disk has you want to install the files from the backup on: blkid
14 - This I did not do, but is recommended: If you are restoring to a new disk, write the backup of grub and the partition table (.grubparts file) to the disk before the fsarchiver restfs step with:
dd if=/mnt/YOUSHOULDKNOW/backup.grubparts of=/dev/YOUSHOULDKNOW
15 - Extract the backup to that drive (and correct partition): fsarchiver restfs backup.fsa id=0,dest=/dev/YOUSHOULDKNOW
(id=0 means that just the first filesystem from the backup will be restored. I am assuming that you did just backup one filesystem with one backup.)
16 - reboot with: reboot
EDIT: I had a problem with "A start Job is running" on startup. I solved this by deleting an old filesystem via Web-GUI of a USB-harddisk that I disconnected, and by commenting a line in /etc/fstab that was referring to a wrong swap-partition. Boot time is now 11 seconds.
Thanks a lot to ryecoaaron for writing this plugin.
Further information regarding the files the plugin is saving:
backup-omv-18-Jan-2019_14-12-01.blkid :: This is the output of blkid put in a file for informational purposes.
backup-omv-18-Jan-2019_14-12-01.fdisk :: This is the output of fdisk -l put in a file for informational purposes.
backup-omv-18-Jan-2019_14-12-01.fsa :: This is the fsarchiver file.
backup-omv-18-Jan-2019_14-12-01.grub :: This is the first 446 bytes of the disk where grub is installed
backup-omv-18-Jan-2019_14-12-01.grubparts :: This is the first 512 bytes of the disk where grub is installed and the partition table.
backup-omv-18-Jan-2019_14-12-01.packages :: This is the output of dpkg -l | grep openmediavault put in a file for informational purposes.