By default, the Snapmirror tcp window size is 1,994,752 bytes. In environments where SnapMirror is used to replicate data using a WAN link, then this setting can actually slow down your replication process. It is important to calculate the appropriate TCP window setting and set it accordingly. Neil Carpenter has a good post on calculating the TCP window size. Basically, it boils down to this:
Window Size = Round Trip Delay X Desired Rate
So if you have a 10Mbps network and the average RTD is 100ms, the window size should be 125,000 bytes.
A couple of points to note about this TCP Window size:
- It is a minimal theoretical window used by SnapMirror and may not be the most optimal window. Try a few variations around this number to figure a good one
- This option sets the TCP window size for all SnapMirror connections. For connection specific window, use the
wsizeoption in the/etc/snapmirror.conffile to specify the window size. - This option needs to be set on the destination filer.
Another option that might aid in the tuning is to enable this option
Options snapmirror.delayed_acks.enable off
This setting turns off the TCP/IP delayed acknowledgments. In high latency networks, this might be beneficial. By default, this option is turned on.
So how do you change the default snapmirror TCP window size? Is it a priv set diag command? A file you have to edit on the filer? A hidden option command?
On the console, issue the command “options snapmirror.window_size X” where X is the window size in bytes.
Thanks Rajeev. You might want to consider editing your article to include that information?
Regards,