This section explains how data flows in VVR and how VVR uses the kernel buffers for replication.

Figure: Data flow with multiple Secondary hosts shows the flow of data for a VVR configuration containing two Secondary hosts with the Primary replicating to one host in asynchronous mode and the other host in synchronous mode.

When a write is performed on a data volume associated with a Replicated Volume Group (RVG), VVR copies the data into a kernel buffer on the Primary. VVR then writes a header and the data to the SRL; the header describes the write.

From the kernel buffer, VVR sends the write to all Secondary hosts and writes it to the Primary data volume. Writing the data to the Primary data volume is performed asynchronously to avoid adding the penalty of a second full disk write to the overall write latency. Until the data volume write to the Primary is complete, the kernel buffer cannot be freed.