Snapshot Replication and Synchronous Replication

There are two types of replication: snapshot replication and synchronous replication. Snapshot replication creates a backup version of your volumes so that you have a point-in-time copy to refer back to if a prior version of the data is needed. Synchronous replication provides a replica of the volumes that is created synchronously with no delay in the recovery point. It is intended for immediate recovery due to a site failure.

To assist in understanding the differences between snapshot replication and synchronous replication, the following table presents a comparison of the two.

Behavior Snapshot Replication Synchronous Replication Notes
Recovery Point Objective (RPO) Depending on the replication snapshot schedule. If the schedule is 15 minutes, then the RPO is 15 minutes 0 RPO
NOTE: RTO can be < 1 minute when in a single site or when metro stretch clustering is not being used.
Failures caused by incorrect writes are not covered by synchronous replication. They can be recovered from snapshots.
Automatic recovery No Yes, if Automatic Switchover is configured Only available with synchronous replication when accompanied by the Automatic Switchover (ASO) feature.
Manual recovery Yes Yes  
Replication Partners Group partners Pool partners Pool partners are auto-generated and deleted when the pool is deleted or merged
Maximum number of partners 2 1  
Number of protected volumes 1024 volumes 512 volumes upstream and 512 volumes downstream
Replication configuration level Volume collection Volume collection Synchronous replication is not allowed on multi-pool volume collections
Maximum number of protection schedules per volume collection 10 10  
Extent of replication The maximum supported number of groups is four Two arrays, two single-array pools
Replication type Between groups Within group
Replicate sub-set of Snapshots Yes Yes
Hardware array models supported All models AFxx, HFxx, AFxxxx, CSxxxx, and HPE Alletra 6000 arrays only For synchronous replication, the upstream array must be the same model as the downstream array
Synchronous mode N/A Soft synchronous mode where when a volume goes out-of-sync, it continues to accept writes
Resume automatically Yes Yes, through an automatic resynchronization
Site fault tolerance Yes Yes
Recovery time objective (RTO) User initiated handover can be completed in under one minute Switchover can be completed in under one minute
Network connectivity for replication traffic between partners IP IP
Support for multiprotocol arrays (Fibre Channel and iSCSI) Yes No
Link bandwidth N/A 10 Gpbs
Number of links At least one. Additional links can be added for redundancy, however traffic occurs over a single IP and port. At least two links are recommended for redundancy and performance
Add support non-disruptively Yes Yes
Remove support non-disruptively Yes Yes
Array replacement allowed Yes Yes, see note
NOTE: To replace an array, un-configure synchronous replication, move data to a new array, then reconfigure synchronous replication.
Changing replication type allowed No No  
Volume resize support Yes Yes, see note
NOTE: To resize a volume with synchronous replication, unconfigure synchronous replication, resize the volume, then reconfigure synchronous replication.
Subnets Arrays do not need to be in the same subnet All arrays must be in the same subnet  
Protection templates Yes None provided
Location of upstream and downstream replicated volumes In separate groups, so in separate volume collections. All in one volume collection
Location of snapshots In separate groups, so in separate snapshot collections. Two separate snapshot collections, one for upstream and one for downstream
Host reconfiguration required after handover Yes No