Re: How to pre-allocate a 4GB File?

[Peter Webb, Toronto Transit Commission]

> 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.