Starting with Release 2.1 of the TS7700, a new synchronous copy mode option was introduced for logical volume replication. Prior to this, the TS7700 Virtualization Engine supported two copy mode options (deferred and immediate) the same as with the 3494 Peer-to-Peer VTS. When data is written to a logical volume in the TS7700 Virtualization Engine, a copy policy is applied through the assigned Management Class and policy settings established at the library. The outboard policy settings indicate in which distributed libraries (or clusters) a copy of the data (logical volume) should exist and how those copies should be made (through immediate, deferred or synchronous replication policies). Copy polices are established based on a customer’s high availability and disaster recovery requirements for their different workloads.

With the deferred (asynchronous) copy mode option, after the job (or application) finishes with the volume, copies of the data (logical volume) are queued for later replication. Then with the immediate copy mode option, after the job (or application) finishes with the volume, copies of the volume are made during demount processing. Though the immediate copy mode option provided customers with more disaster recovery protection than the deferred copy mode option, it didn’t provide synchronous level copy granularity as the data was being written. The synchronous copy mode option provides tape copy capabilities up to synchronous level granularity across two clusters within a multi-cluster grid configuration. Copies to other clusters in the grid can also be made using the deferred or immediate mode copy options. As jobs (or applications) write data to tape, with the synchronous copy mode option, the TS7700 Virtualization Engine will fork the writes to two clusters simultaneously and guarantee dual copy consistency for all data written prior to the last implicit or explicit synchronize operation.

Before the new synchronous mode copy option was introduced, customers would often use their own tape replication methods to guarantee synchronous level granularity which often included using DFSMShsm’s Duplex Tape Support. Now with the new synchronous mode copy option, customers can instead rely on the TS7700 Virtualization Engine to transparently make and access those copies.

For a detailed discussion of the different copy mode replication (deferred, immediate, or synchronous) options refer to the TS7700 Customer Information Center.