What tools to use to analyse slow replication?

[Bostjan]

I have two FreeNAS servers. One server is primary, all data is saved here, it has periodic snapshot tasks for each dataset and replication tasks enabled to replicate all snapshots to second backup server.

The transfer speed of replication is about 150 Mbits/sec.

The only tool to test anything I know is iperf. I’ve tested the connection between these two servers with iperf and it is about 940 Mbits/s.
ifconfig on both servers shows
media: Ethernet autoselect (1000baseT <full-duplex>)

top shows
last pid: 58310; load averages: 1.54, 1.79, 1.81 up 50+16:24:14 09:14:10 140 processes: 3 running, 125 sleeping, 12 zombie CPU: 24.4% user, 0.0% nice, 4.9% system, 0.9% interrupt, 69.7% idle Mem: 275M Active, 434M Inact, 466M Laundry, 6634M Wired, 94M Free ARC: 4109M Total, 774M MFU, 2903M MRU, 27M Anon, 103M Header, 303M Other 3311M Compressed, 7352M Uncompressed, 2.22:1 Ratio Swap: 6144M Total, 899M Used, 5245M Free, 14% Inuse, 4K In

Servers run
FreeNAS-11.1-U4
FreeNAS-11.1-U7

What else can I test? How?
How can I find why the replication is so slow?

 

[Johnny Fartpants]

Things to consider are compression and encryption. Have you got compression turned on for your replication stream and if so which type? Also what encryption cipher are you using, Fast, Standard or Disabled?

What I would also suggest you take a look at 'Display System Processes' during replication on both sending and receiving systems and see if something is hogging CPU such as compression or simply ssh.