We have an EMC SAN for our 1/2 TB financial database on P/Soft. Having high number of prefetch - I have tried num_ioservers values from 10 - 200 and the results vary little. Have anyone heard of this?
I am assuming it may be an EMC bottleneck of some kind since the SAN consists of hundreds of physical disks the NUM_IOSERVERS setting may become irrelevant.
Not sure - just a guess.

We are running Solaris 8 O/S
DB2 7.2 fixpack 6

Thanks
Terry

The bottleneck is probably the number of processors and/or the number of containers per tablespace.

I usually set it equal to the number of containers that reside on separate physical disks per tablespace. For RAID disks, it would be the number separate arrays in a container. If you only have one container in a tablespace, you will get improved performance from the striped EMC SAN, but I don't think DB2 itself will initiate parallel I/O in that situation (for a single query).

It definitely helps if you have at least one processor for each I/O server, although this may not be absolutely necessary. If you have enough processors, then you could set it equal to 2x, 3x, etc the number of containers in a tablespace.