PRIM_REDUCE_ALGORITHM

The PRIM_REDUCE_ALGORITHM keyword specifies a volume selection algorithm to use when primary space reduction is performed.

Syntax

Read syntax diagramSkip visual syntax diagramPRIM_REDUCE_ALGORITHM=LARGESTSINGLESYSTEM

PRIM_REDUCE_ALGORITHM=LARGESTSINGLE|SYSTEM

Operands

The following values are valid:

LARGESTSINGLE
(Default.) Evaluate the available free space on all eligible volumes and select the volume that has the largest single free extent.
SYSTEM
Do not evaluate the free space on the eligible volumes. Use the first volume in the allocation’s eligible volume list.

Usage and processing considerations

  • The PRIM_REDUCE_ALGORITHM keyword applies to non-VSAM, non-SMS allocations only.
  • The LARGESTSINGLE algorithm provides the best chance for the allocation to succeed. However, when the eligible device list contains a very large number of volumes, the elapsed time for the volume selection might be slightly longer.
  • The SYSTEM algorithm will not increase the elapsed time for volume selection. However, the chance that the allocation will fail due to insufficient space is greater, especially for large data sets or volume pools that are heavily utilized or fragmented.

Default

LARGESTSINGLE

Environments

ALLOCATE.

Related keywords

PRIM_REDUCE, PRIM_REDUCE_INC, and PRIM_REDUCE_LIM.

Example

In the following example, the volume with the largest single free extent is selected: 

PRIM_REDUCE_ALGORITHM=LARGESTSINGLE