I have no experience using a RAID with Pro Tools. Yet I think this is a good moment to briefly discuss how RAID works and why it probably is not going to work effectively for audio.
RAID, redundant array of independent disks, is a way where you can take many individual disks and have them work together as a single disk. This can be setup with parity so that if one drive fails, you swap it out and then the other disks use their parity data to rebuild the data that should be on the new disk. It can also be setup without parity, in which case a single disk failing means your data is gone.
RAID is useful for large bandwidth applications, such as uncompressed video capture and playback, where the bandwidth requirements are sufficently high such that a single drive on an interface cannot handle the load, but the interface itself can. As an example, uncompressed standard definition video is 270Mb/s. A single SCSI drive on an Ultra3 SCSI card cannot handle that throughput, but the SCSI card can. Hence, when you stripe four disks together as one on an Ultra3 SCSI card, your large drive can now handle the bandwidth requirements.
The bandwidth requirements for audio are small, relative to video. CD quality audio (44.1kHz, 16bit) is only 1.4Mb/s. Even if you are working with 48 tracks at once, each audio file has a bandwidth demand of 1.4Mb/s. When trying to write files of small bandwidth across multiple disks on a RAID, you lose the edge that RAID gives you because that small amount of data is being written across multiple physical disks. You will incur a greater performance hit simply seeking for the data you need to read/write to the disk.
Give it a try, as I would like to know what happens, but I suspect it will not work the way you hope it will.
__________________-Jonathan S. Abrams, CEA, CEV, CBNT
Apple Certified - Technical Coordinator (v10.5), Support Professional (v10.6 through v10.8)
Vice-Chair, NY Section, AES