This document will explain how to specify the Reduce to Fit variables in all
environments to help to prevent Space-Not-Available (SNA) abends.
And very importantly, how to reset PRI and SEC to their original values
The CA Allocate User Guide, chapter 2, DOES IT FIT (DIF) Support, describes in great detail
how you can dynamically reduce the allocation amounts if the space is not available.
The following is the essential information about RTF.
Both terms, "Does It Fit" and "Reduce To Fit" are used in the User Guide.
I prefer the term "Reduce To Fit" (or just RTF) because it describes what the process is.
RTF can reduce PRImary space quantity in ALLOC & DEFINE and SECondary in EXTEND, EOV and EOV_VSAM,
when a volume in the assigned Storage Group (STORGRP) can't be found with the space needed.
The RTF process utilizes just two simple variables:
SET &RB = nn -- Reduce the PRI/SEC amount by 'nn' percent increments
SET &MP = nn -- Do not reduce the PRI/SEC amount to less than 'nn' percent of the original amount
These Vkgparms would need to be specified to use RTF in these instances:
PLSOPT10 (Y) SMS allocations intercepted in ALLOC and DEFINE
PLSOPT11 (Y) VSAM allocations intercepted in EXTEND.
When the size of SEC has been adjusted for non-VSAM allocations by either RTF or your ASR logic,
you need to reset the value of SEC in EXTEND and/or EOV or the size of the first extent on the next
volume will be the value that was last set by RTF or your ASRs, which could be a very small amount.