Thank you Kris; I think that¹s the piece I was looking for. :) -- Robert P. Nix Mayo Foundation .~. RO-OE-5-55 200 First Street SW /V\ 507-284-0844 Rochester, MN 55905 /( )\ ----- ^^-^^ "In theory, theory and practice are the same, but in practice, theory and practice are different."
On 7/2/09 3:47 PM, "Kris Buelens" <kris.buel...@gmail.com> wrote: > The simple MW approach is surely wrong, it will not create a PAV environment: > Linux will think it has 3 different devices, accidents will happen. > > MDC will avoid the IO; Control Unit cache hit is still IO as concerned for the > z Series, but here PAV would help. AFAIK, PAV will not help if the concurrent > IOs are not satisfied mostly from the control unit cache: the real disk can > only handle one IO anyhow. > > I never implemented PAV (my former customer didn't have PAV enabled for the VM > disks: it wouldn't help with DB2 nor SFS, and that's what they used heavily). > You need to use the MDISK's MINIOPT directory record to tell CP to create a > PAV group; keyword PAVALIAS. This way Linux will recognize all addresses as a > PAV group. My guess: > MDISK 391 3390 1500 500 VOL001 M (I removed the W) > MINIOPT PAVALIAS 1391 2391 > would create 391 as base and 1391 plus 2391 as PAV alias addresses. > > > 2009/7/2 RPN01 <nix.rob...@mayo.edu> >> Your response verifies what I¹d thought was happening, but doesn¹t address >> the whole ³multiple writable minidisk² quandary. >> >> I¹m considering something like the following: >> >> USER LINUXGUEST >> MDISK 391 3390 1500 500 VOL001 MW >> LINK * 391 1391 MW >> LINK * 391 2391 MW >> >> Which would give me three virtual devices all pointing to the same minidisk >> within the Linux guest. >> >> First big question: Have I shot myself in the foot? Common z/VM wisdom says >> that multiple write enabled links to the same minidisk lead down a slippery >> slope to disaster. But would that be the case here? >> >> Second big question: Would PAV see the various I/O requests and assign them >> to separate PAV aliases, allowing for better thorughput to the device? I¹m >> thinking that, if I can get past the first question, then the second would be >> ³yes². >> >> One thing you didn¹t mention in your response is that, hopefully, many of the >> requests can be satisfied from cache, either via MDC or control unit caching, >> avoiding the actual I/O. The thing that PAV and the multiple minidisks would >> give you is the ability to get those I/Os started sooner than with a single >> path in Linux.
