Ed,
MDC is almost always faster than disk cache. First of all, the system
doesn't have to initiate an I/O on your behalf to fetch data from MDC. If
it's not in MDC, it does have to do an I/O, even if the data is found in
controller cache.
If the data happens to be in both MDC and controller cache, the copy in
MDC will be the one that's used. (It's "nearer" to central storage.) Also,
if the data is referenced repeatedly and gets hits in MDC, it's likely to
"age out" of the controller cache (no references).
Marty
____________________
Martin Zimelis
Principal
maz/Consultancy
> -----Original Message-----
> From: The IBM z/VM Operating System
> [mailto:ib...@listserv.uark.edu] On Behalf Of Edward M Martin
> Sent: Wednesday, February 17, 2010 10:41 AM
> To: IBMVM@LISTSERV.UARK.EDU
> Subject: MDC versus Disk CACHE was RE: eliminating locks in VSE
>
> 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
