Diglloyd made some tests using very recent drives and his results confirm the idea that drives have faster and slower areas.
http://macperformanceguide.com/Storage-WhyYouNeedMoreThanYouNeed.html
Also, it's a simple physics problem: given a constant rotational speed ("if" it is constant), angular velocity will be greater on the outer part of the disk. And that means that data can be read/written at a faster rate ("if" the head can read/write that fast).
Can you or tesselator give me different results?
Here's a simple way to look at it. Any mechanical drive does have a variance in throughput on different sections of a platter. That is, the outer most tracks are faster than the inner most tracks.
What I was getting at for throughput, was an
average, that takes both extremes into account. Sometimes you will get faster, sometimes slower. There's multiple dependencies, which can include location on the platter, the data size, as well as the stripe size. Platter location alone doesn't tell the whole story.
You can partition either a single drive, or an array, using them for a performance gain. But what
Tesselator and I communicated about, was the idea of partitioning drives for the software you're running, is based on previous technological capabilities. Older drives where slower, and the RAM was too expensive to be able to load everything into memory.
It's different these days, and is not really valid now. Memory is cheaper, and drives are faster, as well as the other parts of a computer system.
There are situations that using partitions can actually help. Using separate drives is a further improvement. RAID is an even better way to go. Now we've got SSD's in the mix as well. As you improve the overall throughput, so does the cost of the solution.
Separate partitions tend to make things more complicated as well. Particularly for simultaneous access. This is where separate drives come in handy. Any single disk, or RAID array, has a limited throughput. It would be divided amongst the requested files during simultaneous access, not multiplied. That bandwidth is fixed. So splitting up a RAID 0 won't speed up simultaneous access, which would definitely occur (scratch + PS primarily). If you had a separate array for each, that would be another story.
But then again, you can add those same drives to make one array, and get an additional improvement. The average throughput would definitely be increased, as would both the minimum and maximum.
Creating an array, and basing performance on the average isn't perfect, but the easiest thing to do. As it happens, the throughput it can generate, would be more than sufficient for your needs, from the information given. Worst case is better, but will require additional drives and is more expensive. Since you're limited internally for drives, this may not be the best way to go, depending on specifics. (Say worst case, or minimum needed throughput, is 1GB/s. You can't fit that many drives internally (10 drives or more). The best chance would be 4 or 5 SSD's, and it's expensive, limited in capacity, and not the best drive technology for a high write environment).
