Raid is not needed for a recording drive
Its better suited for ur os and software but recording raw wav files u should use a sata or firewire drive, u could use usb 2.0 but I think its a tad slower.
Yes Raid spans a filesystem accross multiple drives but that actually decreases the speed of audio recording. Especially bigger drive around 100 gb, big drives actually have to readjust themselves in order to keep track of where it is because the size of them are huge. Smaller drives are useful in audio recording, even 2 gb ones if u are on the cheap, but I prefer 60 - 20 gb for recording.
I usually do this, make cubase projects on the smaller drive when recording, and then for mastering I usually use the bigger system drive because sometimes I just export the audio, but if I was re routing from a input and out and mastering that way, I would use the recording drive also.
Speed is the biggest thing when recording, not space.