ZFS — Ceph Documentation
https://docs.ceph.com/en/latest/dev/ceph-volume/zfsZFS¶. The backend of ceph-volume zfs is ZFS, it relies heavily on the usage of tags, which is a way for ZFS to allow extending its volume metadata. These values can later be queried against devices and it is how they get discovered later. Currently this interface is only usable when running on FreeBSD.