Write-back protection mode can offer a better performance than write-through protection mode if the replication log resides on high performance storage that is faster than the primary storage. This is because write operations of protected VMs are marked complete upon receiving acknowledgement from the replication log alone. Writes to primary storage are asynchronous and do not constrain JSDR write performance.

To ensure the integrity of data and a high level of performance, it is recommended that write-back protection only be used with an SSD-based iSCSI LUN accessible by both the DRVA and all ESXi hosts of the cluster. Furthermore, safeguards should be implemented to protect data from possible failure of the replication log (e.g., using mirrored RAID). Write-back protection can also be used with VMDK storage; however, iSCSI LUN typically offers the highest level of performance.

Figure 99: Selecting write-back protection mode.

Note: The Write-Back (iSCSI LUN) option will only appear in the drop-down menu when the Protected Domain is connected to an iSCSI replication store.