Hi Willi,
Since you still need iSCSI/NFS/Samba for Windows clients, I think it better to have
virtual ZFS storage backed by Ceph (RBD). I have experience of running FreeNAS virtually
with some volumes for making ZFS pool. The performance is pretty satisfying, almost 10Gbps
iSCSI throughput on 2x 10GbE compute server with 8 volumes of ZFS pool.
Best regards,