Adjusting the TCP window size for SnapMirror

The TCP window size for SnapMirror might have an impact on SnapMirror perfomance. You might have to modify the default value for the TCP window size to suit your network configuration.

Before You Begin

You need to ascertain the round trip delay between the source and the destination for a SnapMirror operation. You also need to determine the bit rate that you would want for the operation.

Considerations

The TCP window size specifies the amount of data that a source can send through a connection before it requires an acknowledgement from the destination for the data received. The default window size for SnapMirror operations is 1,994,752 bytes. The maximum window size for SnapMirror operations is 8,388,608 bytes. You can change the TCP window size to optimize SnapMirror transfers for the network you use.

Note: For example, you can change the TCP window size to the maximum value of 8,388,608 bytes, if you use a 10GbE network for SnapMirror transfers.

Steps

Calculate a TCP window size that works well with the network, using the following formula:
Window Size = (Round Trip Delay) × (Desired Rate)
Example
If the average round trip delay is 100 milliseconds and you want a rate of 10 Mbps, the equation will read:
Window Size = (((0.1 sec) × ( 10,000,000 bps)) / 8) bytes = 125,000 bytes

Therefore, you should set the TCP window size to 125,000 bytes.
Adjust the TCP window size by entering the following command:options snapmirror.window_size rate
rate = the desired TCP window size.
Example
If the desired TCP window size is 125,000 bytes:
options snapmirror.window_size 125000

Parent topic: Considerations for the use of SnapMirror

Related reference

Syntax for snapmirror.conf file entries