same issue with ZFS raidz (used with replication)
we have 6 nic (1GB)
NIC 1 = WEB gui , nodes ip ,
NIC 2 = VM/CT trafic with external,
NIC 3 = cluster dedicated link
NIC 4 = unsused
NIC 4+6 = LAG to PBS server (restore or backup are fast enough for us ;-)
Which link is used for replication ?