mirror-copy not working

[Konrad]

Dear reader, 

I’m running into a problem setting up hammer mirroring that I don’t understand. I’ve set up two filesystems, master on one machine and slave on another. To my understanding, that setup looks good: 

zoii# hammer pfs-status /pfs/hg
/pfs/hg PFS#1 {
   sync-beg-tid=0x0000000000000001
   sync-end-tid=0x000000010e046740
   shared-uuid=7229d076-f45c-11e7-b4cb-010c29f043b1
   unique-uuid=7229d083-f45c-11e7-b4cb-010c29f043b1
   label=""
   prune-min=00:00:00
   operating as a MASTER
   snapshots directory defaults to /var/hammer/<pfs>
}

# hammer pfs-status zoii-hg
zoii-hg	PFS#8 {
   sync-beg-tid=0x0000000000000001
   sync-end-tid=0x0000000000000001
   shared-uuid=7229d076-f45c-11e7-b4cb-010c29f043b1
   unique-uuid=4737dd98-f9d2-11e7-b3fd-3da82a9fd340
   label=""
   prune-min=00:00:00
   operating as a SLAVE
   snapshots directory defaults to /var/hammer/<pfs>
}

ssh communications work well, I’ve also checked that. But:

zoii# hammer mirror-copy /pfs/hg root at 192.168.11.11:/pfs/zoii-hg
Prescan to break up bulk transfer
Prescan 2 chunks, total 4646 MBytes (4818387768, 53692688)
hammer: Mirror-write /pfs/zoii-hg fatal error 22

The only other thing I can find is (on the machine with the slave filesystem)

Jan 15 09:59:27 df1 kernel: hammer_create_at_cursor: CRC DATA @ 900000da3c8d16f0/128 MISMATCH ON PIPE

Master is: DragonFly zoii 5.0-RELEASE DragonFly v5.0.2-RELEASE
Slave is: DragonFly df1 5.0-RELEASE DragonFly v5.0.0.23.g9fea94-RELEASE

What am I missing?

Thank you kindly, 
Konrad