dalethepcman :
Considering that your 5400rps 1tb can do 100mb\s, it is hardly a stretch of the imagination to assume modern 15k sas drives can do 300mb\s.
I keep up somewhat with the top hard drives and I don't think that any hard drive on the market can do 300MB/s. Around 200MB/s, maybe 210MB/s is probably about the fastest we have and they only hit that speed on the outer edge of the disks. Remember, the closer to the center of a hard drive, the slower it is. Closest to the center of each disk is probably less than half of the outer rim's performance.
15K drives don't come in 1TB densities. They probably top out at 300GB, 450GB, maybe some 600GB, but I don't think they go above that. 10K drives can go above, I've seen 900GB 10Ks and I think that I saw a 1.2TB, although it might've not hit the market yet. Also, increasing density does not linearly increase performance.
Increases are more like a square root graph because density increase both by increasing the data that fits in one circle of a disk (called cylinders, this increases performance) and by increasing the number of cylinders (this can help latency very slightly if going from one cylinder to a near by cylinder, but not MB/s). That means that capacity needs to increase by percentage rather than linearly in order to improve performance linearly. Perhaps a better way to say it than square root would be logarithmic.
A drive with lower density is slower than one with higher density if the platter count is the same and the RPM is the same. Going for a lower density means you need to have a much higher RPM to increase speed. High RPM drives have low densities because although they have 3.5" containers, they actually have 2.5" disks instead of 3.5" disks like that 1TB drive.
This means that their platter density is still pretty high, but since the outer edge of the disks move faster than the inner disks (if you are 3.5" away from a center and you are spinning around it, the outer edge spins faster than the inner edge so that they can make one revolution at the same time. This way, the farther you are from the center, the more data is going past the read/write head.
There are simply so many factors that go into hard drive performance, but we can't really make a true 3.5" drive spin at 15K RPM, it spins too fast for such large disks on the current motors and such, there are just problems with it. 15K 2.5" disks are still faster than 7200RPM 3.5" drives, but that is why it isn't as great of a difference as it would be. A 1TB 15K drive could probably hover around 240MB/s, if I were to hazard a guess.
Since we are stuck with 2.5" disks, we can't get as high capacities as 5400, 5900 and 7200 RPM 3.5" drives.
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