The cron job will fail and email you if you have notifications setup. You can also run an archinfo on it - http://www.fsarchiver.org/quickstart/
Thanks for the reply. This is exactly what I needed to know.
I have my head wrapped around this except for 1 thing which might be a stupid question. That is restoring to a new HDD. I need to run the command below to write the backup of grub and the partition table. So will running this command restore the extended & swap partitions like seen by the output of lsblk below.
The more I read what I type the more clear the answer seems, but I want to make sure I don't royally screw up.
dd if=/mnt/YOUSHOULDKNOW/backup-omv-15-Jan-2019_14-12-01.grubparts of=/dev/YOUSHOULDKNOW
Here's the output of lsblk: