MDC works at storage speed; controller cache needs to get out the z. Ages ago (but still a bit valid to see gross orders) Disk = 30 msec CU Cache= 3 msec Storage = xx nsec
An MDC cache hit is also less costly in CPU than a real IO. But, MDC with a very poor hitratio makes you consume too much CPU. Extra advantage MDC: when the wanted data are not in the MDC, CP reads the whole track. Good for sequential processing. bad for random access. Then you might want to look at using RECORDMDC instead (but, I thinks that's only for CMS formatted minidisks, no help for VSE). 2010/2/17 Edward M Martin <emar...@aultman.com> > Hello Rich, > > I am sure that I have asked this question before. > > With the physical CACHE available on most DASD subsystems, is MDC still > a good performance enhancement for MDISK > If you are not paging? > > Or is there a chance of a MDC hit and a Cache hit at the sametime. > > Ed Martin > Aultman Health Foundation > 330-363-5050 > ext 35050 > > -----Original Message----- > From: The IBM z/VM Operating System [mailto:ib...@listserv.uark.edu] On > Behalf Of Rich Smrcina > Sent: Tuesday, February 16, 2010 7:33 PM > To: IBMVM@LISTSERV.UARK.EDU > Subject: Re: eliminating locks in VSE > > On 02/16/2010 06:25 PM, Phillip Gramly wrote: > >> What kind of data? VSAM, SAM, or Libraries? > >> > > mostly SAM. but some VSAM as well. > > > > > > > If your minidisks are taking advantage of minidisk cache, you may be > better off leaving them the way they are. That is, if you have enough > storage available for MDC and aren't doing significant paging. > > -- > Rich Smrcina > Phone: 414-491-6001 > http://www.linkedin.com/in/richsmrcina > > Catch the WAVV! http://www.wavv.org > WAVV 2010 - Apr 9-13, 2010 Covington, KY > -- Kris Buelens, IBM Belgium, VM customer support
