The IBM z/VM Operating System <[email protected]> wrote on 02/18/2010 10:48:52 AM:
> Brian Nielsen <[email protected]> > Sent by: The IBM z/VM Operating System <[email protected]> > > 02/18/2010 10:48 AM > > Please respond to > The IBM z/VM Operating System <[email protected]> > > To > > [email protected] > > cc > > Subject > > Re: Channel Contention > > Being that this is a one-time effort, I wouldn't worry too much about > where the bottleneck is because you indicate can't do anything about it > > anyway. Better is simply to estimate the amount of time it will take to > > some gross level of precision. If you were going to be doing it regularl > y > then it becomes a more important question and could drive configuration > > changes. > > I know tape drives are not involved in your process, but I do know that > > DDR is very effective at driving the channel to them. We have a bank of > 4 > 3590's shared between VM and z/OS on 2 ESCON channels. When I had 2 DDR' > s > writing to 2 of the tapes drives it effectivley saturated the channels > > from the VM LPAR and the z/OS jobs trying to use the other 2 tape drives > > suffered horribly. The reports from Velocity's ESAMAP made it easy to > > diagnose this cross-LPAR interference. (I ended up moving my DDR's to a > > different time slot.) I mention this to say that it will be good that > > there will not be other production workload going on to the DASD when you > > do this. > > BTW, the 3-4% channel utilization I mentioned in my other post is on 2G > > FICON channels. Obviously, 4G or 8G channels would make a big difference > . > > Brian Nielsen I wouldn't rely on those System Activity Display numbers with big IOs to determine channel capacity. That 3-4% is how busy the powerpc processor is in the channel. With big IOs, it's just idling, waiting on the DMA engines. If you add more IOs to the channel, you'll max out some piece of hardware way before the SAD panel shows 50%. With one of my 8 gig FCP channels, I see 25% at max read bandwidth. I think ficon would yield similar numbers. The processor in 2 and 4 gig channels is the same. The processor in 8 gig channels is quite a bit faster. Ray Higgs System z FCP Development Bld. 706, B24 2455 South Road Poughkeepsie, NY 12601 (845) 435-8666, T/L 295-8666 [email protected]
