This section explains how VVR processes an incoming write for a Replicated Data Set (RDS) containing multiple Secondary hosts, some replicating in asynchronous mode and some in synchronous mode.
How data flows in an RDS with multiple secondaries
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In asynchronous and synchronous mode of replication, VVR processes an incoming write as follows:
Note that the Secondary RVG sends the network acknowledgement as soon as the write is received in the VVR kernel memory. This removes the time required to write to the Secondary data volumes from the application latency. On the Primary, VVR waits only for the network acknowledgement from all the synchronous Secondary hosts and not for the data to be written to the Secondary data volumes. This improves application performance. However, VVR tracks all such acknowledged writes that have not been written to the data volumes. VVR can replay these tracked writes if the Secondary crashes before writing to the data volumes on the Secondary or if the Primary crashes before receiving the data acknowledgement.