On Wednesday, 07/28/2010 at 02:38 EDT, Kris Buelens <kris.buel...@gmail.com> wrote: > I dare to disagree a bit: > - MWV is required to get Virtual Reserve/Release, that is sharing inside z/VM. > - SET SHARED ON and FULLPACK Mdisk is for Real Reserve/Release > > They are different beasts: > The Real R/R is a function of the dasd controller: when one system sends a > Reserve, it halts the IOs from other systems. "System" was originally a CPU, > now it can, be an LPAR. Multipathing since XA made it even more complex. One > invented "path groups"; z/OS, z/VM etc send their unique path group id to the > controller and a reserve then locks out all other path groups. > > Real R/R could never help to protect virtual machines from each-other (their IO > come from the same path group ID), so CP has to come in and lock out IO's from > other guests when one guest issued a reserve. That's Virtual R/R. And
> luckily: both can be combined too. I'm not sure what you're disagreeing with me about, Kris. As you say, the "V" allows a guest to use reserve/release CCWs and, as a result, engage CP's protection services for a minidisk. The FP+SHARED configuration causes those virtual reserves and releases to be converted to real ones. If you want to share a RACF database across z/VM instances (LPARs), then you MUST do the following: 1. Define the minidisk as 0-END or via DEVNO 2. Put link mode MWV on the MDISK 3. Configure the RDEV as SHARED in SYSTEM CONFIG If you don't, then RACF will not be able to lock the database from external changes and you will corrupt it. I've seen it happen. If you're not sharing with other LPARs, then all you need is MWV. Alan Altmark z/VM Development IBM Endicott
