Food for thought for the z/VM brain trust:
Background:
We have a IBM Shark 2105-800 with 8GB controller cache. The 8GB is actually
divided into two 4GB pieces - One for each processor in the Shark - and then
1GB is take as NVS so their is actually 3GB of cache available. The shark is
connected to a z890 2086-160 via 4 FICON channels. Shark DASD consists of four
144GB 8-packs and two 72GB 8-Packs.
Software is Z/VM 5.1 and z/VSE 3.1.0. Most of the workload is z/VSE VSAM CICS
and batch VSAM and sequential file processing.
We have MDC enable as follows
q mdc
Minidisk cache ON for system
Storage MDC min=0M max=512M, usage=24%, bias=1.00
Xstore MDC min=1000M max=1000M, usage=19%, bias=1.00
I am trying to determine if an increase in cache memory would improve the DASD
performance.
ESAMON ESASDS2 report for June 2006 shows:(This is a cut and paste from the
SYSTEM total section at the bottom of the report)
<--------DASD Response times (ms)------>
<--Service times--> <--Queueing->
Resp Serv Pend Disc Conn DASD Cntl THR
----- ---- ---- ---- ---- ---- ---- ---
2.1 2.1 0.3 0.8 1.1 0.0 0 0
DISC time is .8 ms
ESASDS5 for June 2006 shows SYSTEM total shows.
<------Total------->
I/O Hits Hit% Read%
37K 28K 74.3 26.8
These figures are consistent for July 2006.
Basically we are seeing 2.1ms DASD response time with .8ms being DISC (cache
miss).
So is 2.1ms good response time for a 2105-800 or would additional cache
actually help?
Thank You
Eric Schadow
Mainframe Technical Support
www.davisvision.com
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