Plenty of other machines have Amazing IO in this day and age now. It is a fairly old notion now that Mainframes were much better at IO than other machines (this /was/ true).
That said, they do deal with IO pretty well. They have dedicated offload processors for transferring data, which means for the same (IO intensive) workload, the CP utilisation of a zSeries machine would be much less than that of an x86, pSeries (or other) machine. And in terms of the disk being a bottle neck... If you're pushing to a disk array that has 192GB (pretty standard) of write-back cache... then no, the disks are not a large concern.
But... At the end of the day, does this really weigh up to the cost of Big Iron, or for that matter the additional licensing of software on top of it?... Not really.. is my answer.
That said, they do deal with IO pretty well. They have dedicated offload processors for transferring data, which means for the same (IO intensive) workload, the CP utilisation of a zSeries machine would be much less than that of an x86, pSeries (or other) machine. And in terms of the disk being a bottle neck... If you're pushing to a disk array that has 192GB (pretty standard) of write-back cache... then no, the disks are not a large concern.
But... At the end of the day, does this really weigh up to the cost of Big Iron, or for that matter the additional licensing of software on top of it?... Not really.. is my answer.