Does RAID improve seek time? If not, considering the files my server will be handling, will the seek times of the SATA RAID configurations be the bottleneck? What kind of transfer rates will the SATA Hitachi's in RAID achieve? How much do these transfer rates play in the overall time?
Onboard RAID controllers tend to be consumer-oriented. They don't perform too well under server conditions. I would only investigate this solution if you have a need for the high capacity that the SATA drives can deliver.
Best solution mentioned. 32-bit PCI will limit sustained transfer rate somewhat, but that's irrelevant with your total throughput needs. You need the high IOPs that the SCSI drive can deliver.
Does RAID improve seek time?
No. In fact, it increases the total access-to-data times.
If not, considering the files my server will be handling, will the seek times of the SATA RAID configurations be the bottleneck? What kind of transfer rates will the SATA Hitachi's in RAID achieve? How much do these transfer rates play in the overall time?
No, the seek times are not really the issue, it's the sustained IOPs that the onboard RAID controller can deliver. Sustained transfer rates may be higher, but that doesn't help you in this situation.
I intend to buy another 15k rpm SCSI and put the two in RAID1. Considering just the one hard drive averages about 100 mb/s average transfer rates, can I expect to achieve an min/average/max of 133 mb/s read rates (bottlenecked by 32bit RAID controller)? How about write speeds? Will the diminish significantly?
RAID 1 (mirroring) typically is done specifically for the redundancy, not for speed increases. Some higher end RAID controllers (LSI, 3Ware) can get somewhat increased read speeds in RAID 1 by intelligently spreading read commands to both drives. Write speeds will always be equal to that of a single drive.
IOPs = I/O operations per second. It's a measure of how many random read/write requests the hard drive can sustain per second. It's the most important benchmark for drives that are being used in a server environment where several applications are accessing the drive at the same time.