Moving data sets with SnapShot

When the source and target devices are in the same RAMAC Virtual Array (RVA) and the data does not need to be manipulated (such as, reblocked, track packed to unlike), DFSMSdss may be able to use SnapShot to quickly move the data from the source location to the target location. SnapShot is much faster than traditional methods, especially when large amounts of data are moved.

To use SnapShot, the following requirements must be met:

The source and target device types must be the same.
The source and target devices must be in the same RAMAC Virtual Array (RVA).
The FASTREPLICATION(NONE) keyword must not be specified.
There must not be any required data manipulation. The following types of processing require data manipulation:
- Reblocking — Reblocking occurs when the REBLOCK keyword is specified or when the VTOC indicates that the data set is capable of being reblocked.
- PDS compression — DFSMSdss compresses a PDS data set during copy, by default. You can specify the NOPACKING keyword to prevent DFSMSdss from compressing the PDS, thereby allowing the use of SnapShot.
- Changing stripe counts — The source stripe count must be the same as the target stripe count for a striped sequential-extended format data set.
- An individual stripe extending to more than one volume — A single-striped extended format data set cannot use SnapShot if either the source data set or the target data set is multivolume.
- PDS or PDSE conversion — Conversion occurs when you specify the CONVERT keyword with these data sets.
- Block-by-block processing of direct access data sets — Block-by-block processing occurs when you specify the RELBLOCKADDRESS OR the AUTORELOCKADDRESS keyword.
- Utilities — SnapShot cannot be used if your data must be moved with a utility.

If the source data is in an RVA, DFSMSdss attempts to allocate the target data set on the same device type in the same RVA, thus increasing the probability that SnapShot can copy the data. If the source data set is multivolume and not contained entirely in one partition of one RVA subsystem, it is not possible to allocate the target so that SnapShot can be used. These data sets are allocated to whatever volumes are available, irrespective of their SnapShot capability.