Scratch Disk and large file opening times

[dave w]

I am using the following hard drives:

1 x 500Gb Hitachi SATA-2 P7K500 Hard Drive- 16MB for Windows XP x64 OS
1 x 320GB Maxtor-Seagate SATA2 7200 - 8MB for Scratch disk

I have 8gb of RAM and a Q9450 processor, Asus P5Q Deluxe motherboard. In Photoshop CS3, if I set the Hitachi drive that I am using for the OS as the scratch disk the opening time for a 880MB file is 6.5 minutes, if I set the scratch disk as the Maxtor the opening time is considerably longer about 10.5 minutes. Why would this be? Could it be the difference in the buffer cache size?

Is 6.5 minutes slow for an 88MB file with many layers? Would I be better off setting up a raid 0 for the scratch disk. Would the cache size matter for this? Would the 2 disks in a raid 0 array have to be identical? And could I have the operating system in a non raid array and then a scratch disk made up of 2 drives configured in raid 0?