Sizing 24-bit storage pools
Article ID: 118851
Updated On:
Products
Issue/Introduction
This article documents the recommended sizing for 24-bit storage pools in IDMS. 24-bit storage is a precious resource and it should be kept to a minimum.
Environment
Release: All supported releases.
Resolution
Historically, storage pool 0 usage was typically about 3000K. In more recent releases, an IDMS CV requires much less. The present recommendation is that pool 0 should be about 1500K, perhaps even smaller. It is also recommended that the CUSHION for all storage pools be set at 10% of the size.
MOD SYS nnCUSHION IS 150STORAGE POOL IS 1500.
In general, other 24-bit storage pools are not required but it can be a good idea to define a pool 1 with the following attributes:
ADD STORAGE POOL 1SIZE IS 500CUSHION IS 50CONTAINS TYPES ( SHARED SHARED-KEPT USER USER-KEPT ).
The reason for this is that if a CV is encountering a short-on-storage condition, having such a pool 1 defined may increase the possibility of the user being able to get into the CV and issue commands to address the situation (cancel tasks, etc). It will also allow the CV to use the High-Performance Storage Protect Option.
If monitoring of a CV determines that a larger pool 0 or 1 is required (for example, if message DC015007 is appearing on a 24-bit pool and not also on the corresponding 31-bit pool), then this should be investigated. It may be that the CV is allocating 24-bit storage unnecessarily - e.g. programs may be compiled with DATA(24) or linked AMODE24, or more likely tasks may be defined with LOCATION BELOW when they should be ANY. Check also that optional bit 227 (force LE storage above the line) is enabled.
Once the 24-bit storage pool sizes have been minimized, also consider increasing FREESTG to minimize the amount of STORAGE RETURNED TO OPSYS in the DC390008 message at startup. This provides the best protection against S878 abends as a result of exhausted z/OS storage due to post startup GETMAINs.
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