On Fri, May 21, 2010 at 11:45 AM, Kris Buelens <kris.buel...@gmail.com> wrote:
> Rob, are you sure CP selects the channel to use? That was the case in the > 370 era. AFAIK, in XA, CP will create a mask telling which channels *can* > be used, but it is the IO subsystem that will select the channel and maybe > even queue the IO if all channels would be busy. In XA mode CP only queues > an IO if it knows the device is busy (ie it launched an IO itself), device > busy due to IO's from other LPARs or CECs will be queued by the IO > subsystem. Thanks Kris. I see my sentence could be read in different ways. I think we agree that CP does not attempt to make the I/O subsystem balance the paths. But I just looked it up and stand corrected about the intentions of the channel subsystem. I was mislead because our DASD subsystem does have a preferred path. "You can specify a preferred channel path to an I/O device. When you do not specify a preferred path, the channel subsystem uses a rotation order for the initiation of I/O requests to a device." Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/
