As my previous posts throughout this forum indicate, I believe that striping is a valuable tool when used in the right situation. I also do a lot of Photoshop work with very large files -- in fact this is my whole reason for being interesting in striping these days.
So, even though I am a fan of properly-used striping, I have to say that the Photoshop components of this benchmark set are not representative of how a power Photoshop user would set up a multi-disk system. Specifically:
In Photoshop the scratch file is the 3rd most important factor determining performance (after memory and CPU, and the speed of the scratch file may even be more important than CPU in many cases). A power Photoshop user would never put his scratch file on a single disk and his CPU and images on a RAID array. If he/she had two disks then the config would be one disk for OS/Programs/Images and the other for scratch. With three disks it would probably be one for OS/Programs/Images and the other two in a RAID0 array for scratch. With four disks it would probably be one for OS/Programs, one for Images, and two in a RAID0 array for scratch.
When reading and writing files, Photoshop does a lot of concurrent disk I/O on the scratch disk and the disk containing the file being read/written. You want these two files (images + scratch) to be on separate spindles.
Yes, heavy usage of scratch file. Again, a Photoshop power user would not set up a machine in the way used in these tests, with the scratch file in a single disk and OS/Programs/Images on a RAID array. That is backwards!
A power Photoshop user would never do this. When doing serious editing it is easy to take up the entire available resources of a fully-configured Windows machine: full 2GB RAM address space fully used up, CPUs maxed out, disks cranking away. A power Photoshop user would shut down all nonessential applications and would never run backups while editing. He/she would *definitely* do backups, but not concurrently with edit sessions.
This is not an important metric for a power Photoshop user, who typically starts Photoshop once then uses it for several hours. However, regardless of whether it is an important metric, the PHotoshop CS startup times would probably be faster if the OS, Programs, and Scratch were on multiple distinct spindles rather than grouped together on a single RAID array. A complete benchmark analysis should include this scenario along with the RAID-only solutions.
I think the point that people are trying to make is that if you've got N disks available to solve a problem, is it better to configure those disks into a single N-disk RAID array (either RAID0, 1, or 5) vs. configuring them as N distinct independent spindles, or perhaps some combination? Most applications will speed up a little bit when going from a single disk to RAID0 -- that is not a surprise. But a true benchmark comparison would include test cases that compare striping vs. multiple distinct spindles as well.
As for the argument that the "the problem with multiple separate disks is that you have to figure out in advance what files go on which disk", I say that yes, this is a problem, but is specifically the kind of problem a *power user* would solve.
Another example: when I was doing full time software development on my machine I noticed that my productivity was often limited by disk I/O time. I did some investigation -- OK, a LOT of investigation -- and ended up configuriung my development machine with four small disks used as follows: one for OS, one for Programs, one for temp files, and one for source code. I chose this configuration because every time I compiled there was significant concurrent I/O to/from each of these four sources. I wanted each of those four sources on seprate spindles to minimize head movement, increase concurrency, etc. Switching to this configuration made a HUGE difference. Would I have set up those four disks in a RAID5 array? No way! A pair of RAID1 arrays? Probably not.
Again, documenting that there are small speedups between a single disk and a RAID array is no big surprise. We would all expect this without even seeing the tests. Comparing a single RAID array to multiple spindles...now that would be interesting.