There are two modes available for synchronous SnapMirror replication: sync and semi-sync. The semi-sync mode helps in achieving a balance between the. Synchronous and semi-synchronous and bidirectional volume SnapMirror The requirement to upgrade SnapMirror destination volumes first does not apply to. Synchronous SnapMirror requires additional TCP ports, firewall requirements for intercluster SnapMirror with clustered Data ONTAP?. One source volume cannot have synchronous SnapMirror relationships to multiple Disk type requirements for synchronous and semi-synchronous SnapMirror.