> > I'm sadly out of touch with mainframe hardware; it seems strange to me > > I can get 120 Gbyte disks for my PC and you folk are using 2.3 Gbyte > > drives on your mainframes. I know the theoretical limit is larger than > > that, and was back when S/360 was announced.
> One advantage to the limited disk size is that since you can only > have one I/O active to a disk volume at one time, spreading data over many > smaller volumes allows more I/Os to be active at the same time. This can > dramatically improve system I/O throughput. IBM even warns that using > 3390-9s can degrade performance, think what using a 3390-120Gigabyte would > do! In the PC world, I believe you can see the same sort of effect by using > RAID0 across multiple volumes, versus one large volume. Locality of reference applies to files, too - 3 3390-3s are not three times better than one 3390-9. PAV is the proper approach. -- Phil Payne http://www.isham-research.com +44 7785 302 803 +49 173 6242039
