On Wednesday, 03/24/2010 at 04:51 EDT, "Ward, Mike S" <[email protected]> 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
