VSAM preallocation

An existing data set qualifies as a preallocated target for a data set copy operation if the cluster name matches and the complete cluster is available on target volumes.

The preallocated data set is usable if all of the following conditions that apply to the data set being processed are met:

The user is authorized to update the target data set.
The cluster types match.
The number of components match.
The key length and offset match.
The KEYRANGES match.
None of the components are multivolume.
Sufficient space is available for each component.
Key sequential data sets (KSDS) are reusable or empty.
Key range data sets are empty.
The data set is cataloged in the standard order of search, if required for the copy operation.
The data set has no alternate indexes or paths defined over it (except for a single path defined directly over the base cluster).

If a target data set is preallocated, it is scratched and reallocated when it is being renamed and:

Any of the following source and target data set attributes do not match:
- CI size
- Record length
- IMBED (only KSDS and key range data sets)
- Key length (only KSDS and key range data sets)
- REPLICATE (only KSDS and key range data sets)
- SPANNED
The data set was not defined as reusable and the high-used relative byte address (RBA) of a target VSAM KSDS is not 0.
The target data set is not large enough to contain the source data set.