I would consider the system thrashing due to dramatic overcommitment of storage by minidisk cache when taking IBM provided mdc arbiter defaults to be a bug.
________________________________ From: The IBM z/VM Operating System on behalf of Rob van der Heij Sent: Sat 4/26/2008 5:19 AM To: IBMVM@LISTSERV.UARK.EDU Subject: Re: newbie question - convert to full pack minidisk On Fri, Apr 25, 2008 at 10:25 PM, Quay, Jonathan (IHG) <[EMAIL PROTECTED]> wrote: > We found a bug in CP minidisk cacheing that would lock up our system. We > turn off MDC at the device level in the system configuration file for our > guest operating system minidisks using RDEV xxxx TYPE DASD MDC OFF. It would take real performance data to conclude on a bug. It may just be tuning. We know that the defaults for the MDC arbiter are such that many systems will favor MDC and thus cause more paging than the MDC hit rate justifies. If the paging subsystem is not properly configured, then that may keep folks waiting or even abend the system. It's a very popular problem at new installations. When the I/O is not eligable for MDC, the arbiter gets no opportunity to favor that, and you avoid the paging. I would prefer to properly configure MDC rather than disable it. And make sure the paging subsystem is able to handle the load when something else makes you page. Rob -- Rob van der Heij Velocity Software GmbH http://velocitysoftware.com/
