I have followed the guides "Installing OMV5 on a R-PI - rev 2.2" and "Getting_Started-OMV5" and I have OMV running beautifully on a Raspberry Pi 4B.
Using the instructions on page 60 of "Getting_Started-OMV5" titled "Full Disk Mirroring / Backup with Rsync" I have a second USB drive with an exact copy of the main drive.
I have setup a scheduled task to run:
rsync -av --delete /srv/dev-disk-by-label-HDD1/ /srv/dev-disk-by-label-HDD2/
every Wednesday morning at 1:00am. All good, so far.
Now, how can I check that HDD2 does in fact contain an exact copy of HDD1 and that I could use HDD2 to retrieve files to my Windows PCs if HDD1 ever failed?