IMAP Replication Slow Performance

[Brady, Mike]

I am looking at using Cyrus IMAP replication as part of setting up a DR 
server at another site but am seeing poor performance during the initial 
sync.

The servers are on different sites connected by a microwave link.  I can 
rsync between the two servers at slightly better than 30Mb/s, but am 
only getting 1.8Mb/s for the Cyrus IMAP replication.

I have set IMAP up as per 
http://cyrusimap.org/docs/cyrus-imapd/2.4.17/install-replication.php and 
the sync does seem to be working.  It is just slow to the point of being 
unusable (there is 100GB of email).

Both systems are up to date Centos 6.5/kolab 3.1 systems.

I cannot see any errors at the network level and as I said I can rsync 
the data just fine.

Anyone got an ideas on what I can look at to determine why this is so 
slow?

Regards

Mike