Synchronous Replication

Synchronous replication enables zero data loss disaster recovery by ensuring that at the time of the update, an identical copy of the primary data is saved to a secondary storage site.  In synchronous replication each input/output update must be acknowledged and confirmed at both the primary and secondary sites. In this way, the system ensures that the copy is always an exact mirror image of the primary data.

The main advantage of synchronous replication is that it delivers zero data loss which means that data is always current. Should operations at the primary site be disrupted for any reason, operations at the secondary site can begin immediately where the primary site left off.

Synchronous replication requires expensive, high performance storage hardware, high performance replication software and high performance synchronous communication lines. Other than the high cost, which limits the affordability of the solution to only the largest of enterprises, the other main disadvantage of synchronous replication is its distance limitation.

The distance between the primary and backup data centers is limited by Fibre Channel, the primary enterprise storage transport protocol, which can theoretically extend as far as 200 kilometers (km) or 124 miles. However, latency quickly becomes a problem as propagation delays lengthen with increased distance. This decreases the distance for synchronous replication to approximately 35-50kms or 20-30 miles which is not enough in the case of wide-area disasters.

Synchronous replication is suitable for companies that, due to the nature of their business and/or government regulations, cannot afford any downtime and require a RPO=0 solution that ensures 100% protection and recovery of their critical information.