About Veritas Volume Replicator network configuration tuning
With Veritas Volume Replicator (VVR), one commonly misdiagnosed problem is an issue with a operating system's network configuration that is mistaken to be an issue with VVR due to replication being slow. To avoid this misdiagnosis, you must be familiar with issues related to network configurations and methods for determining if the issue is with VVR or if the issue is instead with the network.
The following list provides some important concepts related to the health of a network:
A lossy network is a network that tends to lose packets during high network traffic. This loss of packets slows down data transmission due to the packets needing to be resent.
Packet reordering is the inverting of packets during the tramission of data across a network, which causes the TCP receiver to believe that packets are missing. Packet reordering can occur due to multi-path routing, and slows down data transmission due to the TCP receiver requesting the sender to resend packets, which uses more bandwidth when the packets are resent.
The latency of a network is one aspect of the speed of a network, and indicates the delay from the time that a packet is sent to the time that a packet is received.
Some common replication performance issues are as follows:
VVR does not use the full available bandwidth
You observe variations in replication throughput
DCM replay performance better than normal replication
You observe a difference in replication throughput between TCP and UDP
VVR rarely uses the full bandwidth. The maximum replication throughput depends on several factors, such as write size, latency, packet reordering, and packet loss.
You can use the following tools to determine if your network has issues:
If you determined that the issue is with the network and not with VVR, then you must tune the operating system network parameters to improve your network performance.
See Tuning the operating system network parameters.