Yes, this is true. RACF manages the updates to the shared database using the reserve/release functions of the DASD control unit. So, a reserve issued by RACF must flow to the real control unit, so that any reserve issued by another system would be rejected until a release is done. And, CP only issues a hardware RESERVE to a volume only when all of these conditions are met: (a) the device is a full-pack minidisk (b) the MDISK has link mode MWV (c) the device is marked as 'shared' whether by SET SHARED or via RDEVICE statement in SYSTEM CONFIG
A dedicated device works also. CSE (xlink) is *not* sufficient (or required for RACF), because that only controls links to minidisks, not reserve/release on a multiple-write minidisk. On Wed, Jul 28, 2010 at 10:02 AM, Eginhard Jaeger <e.jae...@ch.inter.net> wrote: > Is that really true? When checking just now I found that the 'Planning > and Administration' manual also says so, but I'm 99% sure (allowing > 1% for memory deterioration) that I shared a 20 cyl. RACF database > between two separate VM XA systems and it worked perfectly well. > While the rest of the packs certainly shouldn't be used for any high > activity stuff I believe we did actually use it (space was still quite > expensive 20 years ago). > So I suspect that the 'full pack' requirement may just come from sharing > DASD with non-VM systems, and that it doesn't really apply to the > RACF data base being shared between multiple VM systems only. > But I never had to share disks for later VM releases and so don't know for > sure .. > Eginhard Jaeger > >> From: "Bruce Hayden" <bjhay...@gmail.com> >> > >> That will not work. The database must be on full pack minidisks, >> which means the minidisk must start at cylinder 0 and go to the end of >> the volume. (DEVNO minidisks can also be used.) So, your directory >> entries must be: >> >> MDISK 200 3390 0 END VMRACP MWV READ WRITE MULT >> MDISK 300 3390 0 END VMRACB MWV READ WRITE MULT >> >> The devices must be defined in your SYSTEM CONFIG file as shared. > -- Bruce Hayden z/VM and Linux on System z ATS IBM, Endicott, NY
