This is really the wrong question. Yes, the MDC storage is being used to cache data. The correct question is how long does data sit in MDC without being referenced? If data sits there a week without being referenced, then yes, the MDC storage is being used, but is it effective? (No, there is no way to know how long data has been in cache, IBM tried applying little's law about 10 years ago, but the use of the algorithm was flawed).
MDC storage is a balancing act between paging and I/O. If your page rate is high and hit rate low, then lower MDC storage and vice-versa. MDC can also be tuned by evaluating which disks make better use of it and which users, and either disable specific disks and/or users, or increase specific users share of MDC with the OPTION NOMDCFS. On the ESAMAP report (ESAMDC), there is a field "not ald", or in english, Not Allowed. This is the number of times a user read MDC eligible data but was not allowed to put data into the minidisk cache because the user's MDC fair share was exceeded. This is when OPTION NOMDCFS is used. There is lots of other MDC fine tuning, such as using record caching vs track caching. Record caching increases the effectiveness of the cache, track caching means you get "read-ahead" hits. You could spend weeks doing mdc tuning, but unless you are very storage constrained, without showing much measurable improvement. >Date: Mon, 14 Nov 2005 12:00:16 -0500 >From: Steve Gentry <[EMAIL PROTECTED]> > >Greetings. I have defined 512meg of main storage to be used for >mini disk caching. 0meg from XSTORE. How can I tell how much of >that 512meg is being used or is it assumed that it is all being >used? The QUERY MDC gives the percentage of storage being used >for MDC i.e, 512meg / 6 gig = 12% > >I'm trying to determine if I'm over allocating or under allocating. >Thanks, >Steve > "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 /************************************************************/
