with only 25% of the i/o being reads, more cache won't help too much. Looks like your read/hit is very very low. so the reads are not being cache friendly. Your connect time was the largest component of response time, is faster ficon (express) channels an option? this will decrease response time by 25%. Where if all doubled your read/hit ratio, you wouldn't get that big an improvement. And with 1ms connect time on ficon, this would look like 100k I/O - so assumed to be linux? in which case you are doing great.... The linux workload would explain the data being not cache friendly as linux already caches, you have large mdc, so not much improvements by also caching at a 3rd level in the controller.
>Date: Wed, 23 Aug 2006 14:26:13 -0400 >From: Eric Schadow <[EMAIL PROTECTED]> >To: [email protected] > >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 actuall > help? > > >Thank You > > > > >Eric Schadow >Mainframe Technical Support >www.davisvision.com > "If you can't measure it, I'm Just NOT interested!"(tm) /************************************************************/ Barton Robinson - CBW Internet: [EMAIL PROTECTED] Velocity Software, Inc Mailing Address: 196-D Castro Street P.O. Box 390640 Mountain View, CA 94041 Mountain View, CA 94039-0640 VM Performance Hotline: 650-964-8867 Fax: 650-964-9012 Web Page: WWW.VELOCITY-SOFTWARE.COM /************************************************************/
