PowerFlex uses replicas to protect data within the cluster. In addition, hardware RAID can be implemented to enhance the robustness of individual nodes.
Replicas: Before any write is acknowledged to the host, it is synchronously replicated on an adjacent node. All nodes in the cluster participate in replication. This means that with 2N one instance of the data that is written is stored on one node and another instance of that data is stored on a different node in the cluster. This happens in a fully distributed manner, in other words, there is no dedicated partner node. When a disk fails, it is marked offline and data is read from another instance instead. At the same time data rebuilds of the associated replicas is initiated in order to restore the desired protection level (2N). All nodes participate in the rebuild task. When the failed disk is replaced/revived, the disk is repurposed to resume its original role.
Dell EMC, PowerFlex [SDS]/3.5, Enterprise
Node Failure Protection, Reads/Writes, Data Availability