arcserve-KB : How To Use Iperf to Fine Tune Synchronization and Replication Performance.

Last Update: 2017-12-06 08:29:00 UTC

Description:This document explains the steps to use Iperf.exe utility to fine tune RHA Synchronization and replication performance.

Iperf is a tool to measure the bandwidth and the quality of a network link. Iperf was developed by the Distributed Applications Support Team (DAST) at the National Laboratory for Applied Network Research (NLANR). It is open source software and runs on various platforms including Linux, UNIX and Windows.

 Iperf allows the user to set various parameters that can be used for testing a network and for fine tuning CA ARCserve RHA replication performance.

 Iperf is not ideal for environment which uses Wan Dedupe devices like Riverbed.

CA ARCserve RHA provides several parameters to improve the synchronization and replication performance. The most commonly used options are as below:-

  1. TCP Window size and ChunkLength
  2. Multiple Stream

TCPSendRecvBufferSize sets the TCP window Size for XONET connection. TCP Window size is the amount of data that can be sent without waiting for an acknowledgement from a receiver. RHA uses a TCPSendRecieve Window size (TCPSendRecvBufferSize) of 256K. This parameter can be configured using Ws_rep.cfg file

ChunkLength sets the size of a data chunk used by XONET. If server (Master) and client (Replica) have different chunkLenth configured, the server accepts client’s value. Increasing chunkLength on a fast network may improve replication throughput. It is recommended to configure TCPSendRecvBufferSize as a multiple of chunklength.

Multi streaming is an advanced feature in RHA which allows multiple simultaneous connections from replica to master to accelerate the bandwidth usage.

 Iperf is a command line utility . The commonly used option with Iperf for RHA are as below:-

-s Start as server  ( Always on the Master )

-c start as client ( Always on the Replica)

-w  Window size ( TCPSendRecieve Window size in RHA)

-l   Buffer ( Chunklentgh in RHA)

-p  specificy number of multiple connections ( Streams in RHA)


To start iperf as  server, 

iperf -s

To speficy a client to connect to server

iperf -c


To start Iperf with 256K Window size and 64 chunklentgh ( default values in RHA) on the master


Execute the following command on the replica to connect to master with 256 K window and 64 K chunklentgh


Once the analysis is done, iperf displays the result as follows:-



You can change TCP Window Size and chunklentgh ( It is recommended to configure TCPSendRecvBufferSize as a multiple of chunklength) and run several checks to identify which one gives you the better throughput. you can then replace the current values (TCPSendRecvBufferSize and chunklength) in ws_Rep.cfg (both on the master and replica with the optimum values).  Any changes in ws_rep.cfg does require an engine restart .

Multi streaming is an advanced feature in CA ARCserve RHA which allows to establish multiple connections from replica to master ( Multiple streams) to speed up the data transfer. This is ideal for WAN Environment with high latency.

Iperf can be used to check whether enabling mutiple streams in your network can accelerate the data transfer . The following command can be used to force iperf to use multiple connections from Replica to master.


The following result shows enabling multiple streams in Local Area network is not ideal



Follow the below technical article to configure the streams:-




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    Komail Mookhy

    iperf -c IPaddress -w 256000 -l 64000