Moving Data with SnapShot

SnapShot is a function of the RAMAC Virtual Array (RVA). SnapShot allows you to make a very quick copy of a set of tracks (an entire volume, a data set, or a random set of tracks). The copy operation is completed with only a few I/Os to the device.

DFSMSdss provides two types of SnapShot services:

Native SnapShot: Data is snapped (quickly copied) directly from the source location to the target location. This function occurs when you issue a DFSMSdss COPY command to copy volumes, tracks, or data sets from one DASD volume to another. DFSMSdss uses this method whenever the source and target data are on like devices in the same partition on the same RVA subsystem, and no reblocking is required. DFSMSdss can use this method whether the CONCURRENT keyword is specified. With SnapShot, the copy of the data is logically and physically complete as soon as the snap is complete.
Virtual Concurrent Copy: Data is snapped from the source location to an intermediate location and then gradually copied to the target location using normal I/O methods. This method operates in a fashion almost identical to the existing concurrent copy (CC) operation. All DFSMSdss users and callers of the DFSMSdss application programming interface (API) (such as DFSMShsm, DB2®, and IMS™) can continue to use and receive the services of the functionally identical concurrent copy operation. Using virtual concurrent copy, the copy or dump of the data is logically complete after the source data is snapped to the intermediate location. The processing is physically complete after the data has been moved to the target media. It is also possible to perform concurrent copy on VM minivolumes using virtual concurrent copy.