zvols on linux have known performance problems, see https://github.com/openzfs/zfs/issues/7631 https://github.com/openzfs/zfs/issues/7631 -- most VM disk images

zvols on linux have known performance problems, see https://github.com/openzfs/zfs/issues/7631 https://github.com/openzfs/zfs/issues/7631 -- most VM disk images on ZoL end up being regular files, for this reason. zfs send+receive of those such work just fine, but the bigger problem is that zfs replication doesn't know about the "pull on demand, migrate in the background" design at all, so you're probably better not using it for migration.