Hi Martin,
Thanks for "paging" me. It is good to hear from you, and I hope that all
is well!
CPExpert has 16 checks (I call them "rules") related to potential
performance problems with the paging subsystem. Included are checks
whether allocation percent exceeded guidance, checks for whether different
allocation sizes were defined for page data sets (unbalanced allocation),
and checks for significantly different I/O response time for different page
data sets (unbalanced access times).
When Message IRA205I (50% AUXILIARY STORAGE ALLOCATED) was introduced with
z/OS V1R8, I took note only because a system message was produced at 50% or
more of allocation of all available slots in the auxiliary storage paging
space. Since the message documentation said "System Action: Processing
continues" and there was no indication of any further system action, I
assumed that Message IRA205I was simply a routine performance alert. The
System Programmer Response was "You should consider adding additional page
data sets to your system. When utilization exceeds 30%, the slot allocation
algorithms become less efficient, and may degrade I/O performance." It
appeared that IBM felt sufficiently concerned about using significantly
more than 30% auxiliary storage that this new message was
introduced. Since this message was introduced concurrent with significant
changes to real memory control in z/OS V1R8, I assumed that there was
increased wmphasis on the 30% ROT because of these z/OS V1R8 changes. I
did include a discussion of Message IRA205I in CPExpert user documentation,
and I noted that the z/OS message would be produced every 2 hours so long
as the condition existed.
The discussion in Message IEE711I "If the reason field shows A CRITICAL
AUXILIARY STORAGE SHORTAGE EXISTS...SVC dumps will not be allowed again
until the auxiliary storage utilization drops below 35%...." was added with
z/OS V1R11. Regardless of whether this 35% is too conservative, there
appears to be continued justification for retaining the ROT of keeping
auxiliary storage allocation below 30%, and Message IRA205I was a
potentially serious warning of an unwelcome system effect with
over-allocation of auxiliary storage. It is almost moot whether the 30%
ROT relates to the slot allocation algorithms becoming less efficient,
since some system functions demand that a significant percent of auxiliary
storage must be available.
Best regards,
Don
******
Don Deese, Computer Management Sciences, Inc.
Voice: (804) 776-7109 Fax: (804) 776-7139
http://www.cpexpert.org
******
At 04:29 PM 2/5/2012, you wrote:
Paging (if you'll pardon the pun :-) ) Don Deese and wondering what
checks he has in CPExpert in this area. Might provide inspiration to z/OS
Development - if Barbara's comment had spurred them to revisit this area.
Cheers, Martin
Martin Packer,
Mainframe Performance Consultant, zChampion
Worldwide Banking Center of Excellence, IBM
+44-7802-245-584
email: martin_pac...@uk.ibm.com
Twitter / Facebook IDs: MartinPacker
Blog:
https://www.ibm.com/developerworks/mydeveloperworks/blogs/MartinPacker
I
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