Determine Replication Throughput Parameter

Two parameters most often used to adjust replication throughput:

Window Size

This is the transport window for the IPStor SAN/IP protocol. The window size is in packets (1500 bytes). The default value is 320, for a window of about 480KB. FalconStor suggests a setting of 1024 for a window of about 1.5 MB. The total window size of data will not actually be sent unless it is generated by outstanding replication commands. Therefore, it doesn't hurt to make this a little larger than necessary.

The following formula can be used to figure out the best possible parameters for window size:

Window-size=Line speed (T1, T3, and OC3)*Latency (millisecond)*1.2(Overhead latency)*2(roundtrip)/1.5

Based on the formula above and a series of tests, we recommend using the default setting for T1 line. It is more than enough to handle even 100ms latency.

For a T3 line, the default setting is also recommended for most cases. If the latency is greater than 50ms, the recommended window-size=1024.

For OC3 line, if the latency is greater than 50ms, the recommended setting will be window-size=4096. However if the latency is greater than 10ms and less than 50ms, the use of such setting may not achieve the best performance. The recommended setting in this case is window-size=640.

Replication-cmdsout

This parameter controls how many outstanding commands are sent by the source IPStor server during replication. The default value is 4. Each command is 64KB in size, so the default is 256 KB of outstanding data. Make sure to specify an appropriate value that keeps the channel full of data.

The following formula can be used to figure out the best possible parameters for replication-cmdsout:

Cmdsout= Line speed (T1, T3, and OC3)*Latency (millisecond)*1.2(Overhead latency)*2(roundtrip)/64

Based on the formula above and a series of tests, we recommend using the default setting for T1 line. It is more than enough to handle even 100ms latency.

For a T3 line, the default setting is also recommended for most cases. If the latency is greater than 50ms, the recommended cmdsout=24.

For OC3 line, if the latency is greater than 50ms, the recommended setting will be cmdsout=84. However if the latency is greater than 10ms and less than 50ms, the use of such setting may not achieve the best performance. The recommended setting in this case is cmdsout=12.

Check the actual window size and replication activity: cat /proc/krudp

The line speed used in the above formulas is MB/s not Mb/s. The latency is one way only. If using the round trip latency, drop the *2 in the formula.

The window size is changed at the server level in the IPStor Console. Right click on the IPStor server name and open the properties window. Under the performance tab, set the window size.

To change the cmdsout, pull down the help menu on the top line bar of the IPStor Console and click ABOUT. Hit the TAB key until the OK button is highlighted. Type sysvar , this will open the system variable window where the replication cmdsout parameter can be adjusted.