To understand how replication works, we must first consider the basic PowerFlex architecture.
The following base elements are the foundation of PowerFlex software-defined storage, a platform that scales linearly to hundreds of SDS nodes:
When considering architectural options for replication, maintaining the scalability and resiliency of PowerFlex is critical. The replication architecture in PowerFlex is a natural extension to the core elements.
PowerFlex version 3.5 introduced a new storage software component called the Storage Data Replicator (SDR). Figure 3 depicts where the SDR (light blue “R” icon) fits into the overall PowerFlex replication architecture. Its role is to proxy the I/O of replicated volumes between the SDC and the SDSs where data is ultimately stored. Write I/O operations are split, sending one copy on to the destination SDSs and another copy to a replication journal volume.
Sitting between the SDS and SDC, from the SDS point-of-view, the SDR appears as if it were an SDC sending writes. From a networking perspective, however, the SDR-to-SDS traffic is still back-end storage traffic. Conversely, to the SDC, the SDR appears as if it were an SDS to which writes can be sent.
The SDR mediates the flow of traffic for replicated volumes only. Nonreplicated volume I/O operations flow, as usual, directly between SDCs and SDSs. As always, the MDM instructs each SDC where to read and write its data. The volume address space mapping, presented to the SDC by the MDM, determines where the volume’s data is sent. But the SDC is ignorant of the write-destination as an SDS or an SDR. The SDC is not aware of replication.