Disadvantages of synchronous mode replication

Synchronous mode replication can impact server performance due to latency issues and link constraints. Consider the following:

  • The write I/O service times on the primary and secondary systems

  • The time to move the data across the link is a function of the link latency, link speed, and the number of buffers available on the link

As the distance between the primary and secondary storage systems increases, the latency also increases. For example, a one-way distance of 100 kilometers over dark fiber adds approximately 1 ms to the write latency.

Even with the primary and secondary storage systems located side-by-side and linked by an FC SAN, using synchronous mode volume groups adds latency to a host write because the write must be committed on both systems before the IO complete is sent to the server.