When you use UDP as the replication protocol, Veritas Volume Replicator (VVR) uses its own network flowcontrol. VVR increases or decreases the rate at which data is sent depending on the number of timeouts or memory errors it gets per second. If the number of errors is greater, VVR decreases the sending rate to avoid network congestion. If there are only a few errors or no errors, VVR continues to increase the sending rate by a fixed amount every second. For a lossy network, a large number of errors may occur, which prevents VVR from increasing the sending rate. However, these errors are not due to network congestion so VVR should continue to increase the sending rate.
You specify the error tolerance VVR uses by setting two tunables: vol_rp_increment and vol_rp_decrement. VVR increases its sending rate if timeouts or memory errors per second are not more than the vol_rp_increment value. VVR decreases its sending rate if timeouts or memory errors per second are more than vol_rp_decrement. The default value of both tunables is 8.
In the case of a lossy network, the sending rate does not increase because the number of errors per second could be more than vol_rp_increment or vol_rp_decrement, and the sending rate can decrease further. This impacts replication performance. If RLINK statistics show a higher number of errors and VVR is not using available bandwidth, you may be able to improve replication performance by tuning vol_rp_increment and vol_rp_decrement to higher value like 16 or 32. In the 5.1 SP1 release and later, you can change both tunables using the vxtune command. This tuning is required only on the Primary host.