Thanks bvrulez for the handy restore tutorial.
The drive in my OMV server died and I replaced it with a different make & capacity drive. The dd grub restore recreated the old drive's partition tables (didn't expand to the larger drive's size) which was ok with me. However when booting it returned "Invalid partition". I tried the steps 3-4 times with variations in the destination device naming. This is what I believe to be correct after re-reading numerous materials --
dd if=backup.grubparts of=/dev/sda
fsarchiver restfs backup.fsa id=0,dest=/dev/sda1.
But it still wouldn't boot. I also tried grub-install to manually reinstall grub. It was never able to boot.
Eventually I re-installed OMV from scratch, then booted from the USB SystemRescueCD and used fsarchiver to restore the system files. That initially seemed like the longer route, but it ended up being much easier and ultimately the only path that worked for migrating to a new drive. The dd grub restore isn't able to handle new drives.