Go over to the sound on sound archive ... there are articles galore on the subject . You need to partition the HD and make this your "current projects " area . The first area where you set up a logical partition will be on the outside of the disk , which also happens to have the fastest seek and read and write times.If you run a sampler then put all your samples there too .
Aslo , If you look at a typical HD that is one giant partition with the OS and all ; after awhile the de-fragment map generated is full of little areas designated as "system " and in a FIXED POSITION!! you don't want that in the middle of a sample file ..
Go track down the sos article(s ). Everything you need to know is there .
Cheers