Rob:
So, if the shared disk does NOT start ay Cyl 0 but at Cyl 1, the MWV is worthless and I cannot share disks?
I think what I need to understand is: who says CP has to issue any reserve/release? Does not VSE (via the lock file or some internal locking mechanism) handle this? Why does CP need to be involved?
BTW, there are no LPARS involved here. And the reason why not all shared packs start on cyl 0 is because we wanted to retain uniqueness of DASD volids whenever possible. Thus, the VSE DASD starts at REAL CYL.
David Wakser
-----Original Message-----
From: Rob van der Heij [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, September 06, 2006 11:33 AM
To: [email protected]
Subject: Re: VM directory entry for shared DASD
On 9/6/06, Wakser, David <[EMAIL PROTECTED]> wrote:
> Please settle an argument: if a DASD volume is to be shared in
> WRITE mode between two VSE systems running under VM, should the MDISK
> statement specify MWV or MW?
Why settle... can we not just disagree? ;-)
If you have multiple systems on the same z/VM, you need MWV to make sure that CP will intercept reserve / release and emulate it. You could not have all virtual machines do real reserve release because the hardware would not be able to distinguish between virtual machines (only sees which LPAR does it).
When the virtual machines are on different LPARs (or machines) you need the disk to start at cylinder 0 to ensure that CP will indeed pass the reserve/release to the real device (and I am not sure whether you have to define it as SHARED in the configuration file, but you prolly want to disable MDC anyway).
When you more than one VSE in the z/VM LPAR and another one outside the LPAR (native or under z/VM, same machine or other machine) you need MWV *and* start at cyl 0 to make sure that CP will keep the guests apart, and will issue the real reserve/release that comes from that.
Rob
--
Rob van der Heij
Velocity Software, Inc
http://velocitysoftware.com/
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