Can I put existing already half-full EXT4 discs into an OMV system, without reformatting?

I have a small slow PC I'm using as a backup server, running Mint, with a couple of EXT4 already half-full 3T drives, from which I rsync from one to the other for security, rather than use explicit RAID. Reading what OMV includes, I figure it may be quicker for me to switch to OMV than figure out how to get the other goodies working under Mint. I would intend to keep the discs as JBOD with rsync. Once OMV is installed, will I need to reformat and re copy the data to the drives, or will OMV be happy with pre-formatted, half full drives? If the worst comes to the worst, I can fit one drive, format it, copy the data from the other, but that seems a bit of a waste of time if OMV can get on with half-full drives. All the guides I've read ignore this aspect, and assume you'll be starting with new drives.

Thanks both. I hoped and expected that was the answer, nice to have it confirmed.