Alan, With it not being a full-pack as Mike mentioned in his post, there would always have to be CCW translation, would there not? The question is whether that is a significant hit compared to the full pack including Cyl 0. Considering that, in the olden days, CP overhead was quite high compared to today, the performance hit, while there, might not be sufficient to be a cause of concern.
Regards, Richard Schuh > -----Original Message----- > From: The IBM z/VM Operating System > [mailto:ib...@listserv.uark.edu] On Behalf Of Alan Altmark > Sent: Wednesday, March 24, 2010 8:08 PM > To: IBMVM@LISTSERV.UARK.EDU > Subject: Re: initializing z/Linux disks > > On Wednesday, 03/24/2010 at 04:51 EDT, "Ward, Mike S" > <mw...@ssfcu.org> > wrote: > > I thought there was overhead in specifying it as a minidisk rather > > than a dedicated full disk. The overhead would be in the > translation > > of the I/O addresses and such. You know like linux reading > cyl 0 when > > it's really cyl 1 etc.... Is there still that type of > overhead in VM? > > Back in the native-mode days, there would be I/O assist for > dedicated devices that wouldn't be provided to a full-pack > minidisk. In an LPAR, the I/O assist isn't available to CP > (LPAR is using it), so CP is already handling the guest I/O. > Eric or Steve will have the definitive answer, but I > speculate that full-pack minidisks and dedicated dasd > generally take the same shortcuts for geometry issues. E.g. > no need to modify cylinder numbers. > > I'm guessing one of big differences, however, is the lack of > minidisk cache (MDC) for dedicated devices. In some cases > that's a help and others a hinderance. If it hurts, we give > you the ability to turn off MDC for a minidisk. > > Alan Altmark > z/VM Development > IBM Endicott >
