You can use either concurrent copy, virtual concurrent copy, or FlashCopy® to make point-in-time copies that can be used for backup operations. DFSMSdss uses concurrent copy and virtual concurrent copy for data sets that span a 3990 Model 6 Storage Control, RAMAC Virtual Array subsystem, or ESS.

With concurrent copy, DFSMSdss works with a cache-capable 3990 storage control and SMS to begin and sustain concurrent copy sessions. DFSMSdss determines a list of physical extents by volume that are associated with each session. For each backup session, the storage control ensures that the original track images are preserved in the cache, while writing any updated track images to DASD. Each cache-capable 3990 storage control can sustain up to 64 concurrent copy sessions simultaneously.

When virtual concurrent copy is being used for backup, DFSMSdss uses the SnapShot feature of the RAMAC Virtual Array to create an interim point-in-time copy of the data to be backed up. Once the point-in-time copy is created, serialization is released and the concurrent copy session is logically complete. DFSMSdss then performs I/O from the interim point-in-time copy to create the backup. Once this is done, the backup is physically complete and the job ends. Similar operations are followed for ESS.

You specify whether concurrent copy should be used when backing up data sets or volumes using DFSMSdss. A point-in-time session is established when DFSMSdss is called for volumes or data sets allocated behind a storage subsystem that supports concurrent copy or virtual concurrent copy. The data set's management class controls concurrent copy usage. To use virtual concurrent copy, you must have an ESS or the SnapShot feature enabled on the RAMAC Virtual Array and the DFSMSdss concurrent copy SnapShot SPE installed.

With DFSMSdss SnapShot copy support and the RAMAC Virtual Array, you can make almost instantaneous copies of data. Once the copy is complete, both the source and target data sets or volumes are available for update.