Setup TrueNAS Backup Server

Im looking to do a TrueNAS backup server. I have setup and moved my data to the new TrueNAS main server and have my old unraid server still kicking around for now. If I have a bunch of hdds from my old unraid server 2x14tb,4x12tb and 4x8tb can I just do mirror vdevs with all the drives in TrueNAS? Or can I do the ZFS snapshots to my old unraid server (if thats possible)? Leave my unaid server running and use syncthing to unraid server?

I don’t use Unraid but I know they have some kind of ZFS support so there might be a way to send a snapshot to it.

If there is space in the system you can put the drives in your TrueNAS and have a separate pool made of them.