On 3/19/07, Kris Buelens <[EMAIL PROTECTED]> wrote:
I guess that what you found is that VSE adheres to the old rules: it is useless to send an I/O to a disk that is busy, so VSE queues. VM can't change that.
In that case, it might help to give VSE its disk space in less than full pack mini disks so that there are more virtual subchannels per GB (only make sense if the workload in VSE is such that you would end up with I/O spread over those smaller disks).
Minidisk cache can help or hurt VSE: CP's MDC will change the IO to make it a fulltrack read. So if you work sequentially, it will help. I you work randomly the fulltrack read will probaly not help. With high I/O rates it will even hurt due to the larger data transfers.
For random I/O with small block size you might enjoy recordmdc but you would need your data sufficiently grouped to do that. For full track cache, you probably will not notice the larger data transfers if you're on FICON, but there is also CPU cost associated with MDC, and if you don't save I/O by MDC then spending CPU cycles and memory makes less sense. If the z800 has a lot of available memory (quite possible with one z/VSE guest) then MDC could help reduce some I/O and maybe speed up some things. Again, for this it could also help if you spread your datasets over different mini disks. That way you can still read data out of MDC while waiting for a write to complete. Rob -- Rob van der Heij Velocity Software, Inc http://velocitysoftware.com/
