Something you may want to look in to is call short stroking
excerpt from Tom's Hardware - Accelerate Your Hard Drive By Short Stroking
Short stroking aims to minimize performance-eating head repositioning delays by reducing the number of tracks used per hard drive. In a simple example, a terabyte hard drive (1,000 GB) may be based on three platters with 333 GB storage capacity each. If we were to use only 10% of the storage medium, starting with the outer sectors of the drive (which provide the best performance), the hard drive would have to deal with significantly fewer head movements.
The result of short stroking is always significantly reduced capacity. In this example, the terabyte drive would be limited to 33 GB per platter and hence only offer a total capacity of 100 GB. But the result should be noticeably shorter access times and much improved I/O performance, as the drive can operate with a minimum amount of physical activity.
The main idea is to partition the hard drive and only use the outer portions of the platters to reduce seek times.
I use this on my os hard drive, and use the remainder of the hdd for data storage that is not accessed often. This may not work as well for you if you plan on using data from the whole drive often, but it may be something to look into.