VVR replicates in synchronous and asynchronous modes. In synchronous mode, a write must be recorded in the Primary SRL and posted to the Secondary before the write completes at the application level. When replicating in asynchronous mode, an update to the Primary volume is complete when it has been recorded in the Primary SRL. The decision to use synchronous or asynchronous mode must be made with an understanding of the effects of this choice on the replication process and the application performance.
You can set the mode of replication between the Primary and each Secondary depending on your requirement. You can replicate to the Secondary hosts of an RDS in different replication modes.
In each mode, VVR replicates and completes the application writes differently. Each mode deals differently with network conditions. The following sections provide a brief description of synchronous and asynchronous modes of replication and discuss some of the issues involved in choosing between the two.