Synchronous mode ensures that a write has been recorded in the Primary SRL and posted to the Secondary before the write completes at the application level. In synchronous mode, the data on the Secondary is completely up-to-date and if a disaster occurs at the Primary, data can be recovered from any surviving Secondary without any loss. If the Secondary must reflect all writes that have successfully completed on the Primary in the case of a disaster, synchronous mode is the correct choice.
Synchronous replication keeps the Secondary up-to-date with the Primary by waiting for each write to reach the Secondary before the application sees the successful completion of the write on the Primary.
Synchronous replication provides data currency but can impact application performance in high latency or limited bandwidth environments. When using synchronous replication, the response time experienced by the application is affected because the write has to wait for the Secondary to acknowledge it before the write can complete on the Primary.
Synchronous replication is most effective in application environments with low update rates. However, it can be deployed in write-intensive environments where high bandwidth, low latency network connections are available.
The performance of synchronous replication could degrade significantly if the peak application write rate exceeds the available network bandwidth. The amount of degradation can be reduced by increasing network bandwidth and reducing network latency between the Primary and Secondary. Refer to the Veritas Volume Replicator Planning and Tuning Guide for a discussion of network latency and network bandwidth, and their effects on VVR performance.