Sizing 24-bit storage pools

Document ID : KB000118851
Last Modified Date : 02/11/2018
Show Technical Document Details
Introduction:
This article documents the recommended sizing for 24-bit storage pools in CA-IDMS.
Background:
24-bit storage is a precious resource and it should be kept to a minimum.
Environment:
CA IDMS, all supported releases.
Instructions:
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 nn
CUSHION IS 150
STORAGE 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 1                                      
SIZE IS 500                                         
CUSHION IS 50                                       
CONTAINS TYPES ( SHARED SHARED-KEPT USER USER-KEPT )
.

The reason for this is that if your CV is encountering a short-on-storage condition, having such a pool 1 defined may increase the possibility of your being able to get into the CV and issue commands to address the situation (cancel tasks, etc).

If monitoring of your CV determines that you need a larger pool 0 or 1, then you should investigate why.
It may be that your system is allocating 24-bit storage unnecessarily - e.g. tasks may be defined with LOCATION BELOW when it should be ANY.

Once you have minimized your 24-bit storage pool sizes, also consider increasing FREESTG to minimize the amount of STORAGE RETURNED TO OPSYS in the DC390008 message at startup.
This gives you the best protection against S878 abends as a result of exhausted z/OS storage due to post startup GETMAINs.                    
Additional Information:
SYSTEM Statement
STORAGE POOL Statement
KB000105997 - What makes up the REGION NEEDED TO STARTUP storage?