Thanks everyone, I have a better understanding of how it works now. On Wed, Mar 2, 2011 at 4:28 PM, Eric R Farman <[email protected]> wrote:
> Tom, > > As Rick states, it depends on both software and hardware. From our side, > z/VM's EDEVice support is entirely multipath capable. An EDEVice created > and brought online with a single path can be modified via command to have > multiple paths. Those new paths will immediately be usable for I/O directed > to the device, presuming it was a valid connection. > > > There is then the question of what VM does with those four paths. > > Does it perform some kind of rotation, spreading the I/O load? Or do > > the other paths serve only for fail-over? > > z/VM does a round-robin on all available (accessible at VARY ON time) and > healthy (no SAN failures) paths across an EDEV. Paths that are deemed > "sick" for some reason (SAN events, I/O errors, etc.) are temporarily > removed from the path selection criterion while they undergo the appropriate > error recovery. The exception to this rule is the ATTRibute sets for the > DS6800 (ATTR 1750) and SAN Volume Controller (ATTR 2145), where we > round-robin on the healthy paths connected to the preferred half of those > boxes and use the non-preferred paths for failover purposes. > > Regards, > Eric > > Eric Farman > z/VM I/O Development > IBM Endicott, NY
