Migrating to ZFS

I recently purchased a used PowerEdge R420 rack server with a Compellent SC220 Storage Shelf. I currently have four 3.5" HDDs in the R420 and ten 2.5" HDDs in the SC220. The R420 server previously had TrueNAS installed, so all of the hard drives on both the R420 and the SC220 are formatted with ZFS. I'm now running Ubuntu on the...