The TCP window size for SnapMirror might have an impact on SnapMirror performance. You can change the default value of the TCP window size to suit the network configuration. You can specify the window size for a particular SnapMirror relationship by modifying the corresponding entry in the snapmirror.conf file.
|Connection type||Default TCP window size||Maximum TCP window size|
|Single path||1,994,752 bytes||7,340,032 bytes (7 MB)|
|Multipath||1,994,752 bytes||14,680,064 bytes (14 MB)|
window size = (round-trip time) × (available bandwidth)
If the average round trip delay is 130 milliseconds and the available bandwidth is 200 Mbps, the equation is:
window size = (((0.13 sec) × (200,000,000 bps)) / 8) bytes = 3,250,000 bytes
Therefore, you should set the TCP window size for the SnapMirror relationship to 3,250,000 bytes.
Similarly, you can calculate the optimal TCP window size for different round-trip time and bandwidth values. The following table provides a few examples:
|Round-trip time||Available bandwidth||TCP window size to maximize throughput|
|120 ms||400 Mbps||6,000,000 bytes|
|100 ms||1000 Mbps||12,500,000 bytes (can be used only for a multi-path SnapMirror relationship)|
|50 ms||155 Mbps||968,750 bytes|
value is the required TCP window size (in bytes), as calculated in the preceding step.
The following entry specifies a TCP window size of 3,250,000 bytes for the SnapMirror relationship:
The following entries specify a TCP window size of 3,250,000 bytes for the multipath SnapMirror relationship: