Hi,
The reason that you don't see many drives that do internal stripping stems from the fact that in most modern HDs, all of the heads are mounted on a single actuator. What this basically means is that any time a seek is required, the entire actuator arm moves causing the heads to move as well. If the platters were perfectly aligned, it wouldn't be a problem to do reads/writes of the same track on each of the platters in parallel, but unfortunately this really isn't possible. As platters spin, they actually change shape based on how fast they are spinning. In addition, platters at the top of the drive tend to have a different temperature than platters at the bottom of the drive. As a result, it would be fairly disasterous to try and read data from each head on the same actuator.
A way to get around this is to use multiple actuators, and have multiple heads per platter. This is what the seagate ST12450W did about 5-6 years ago. It has 2 heads per surface, with 4 heads per platter, using 2 actuators to stripe the data. It was only a 7200 rpm drive with fairly small platter density, but was only beaten 3-4 years later with the advent of the 10K rpm cheetah drives. The problem was that it's not cheap to add new actuators, heads, logic, etc, and the drive ended up not being very economcial so seagate eventually canceled it.
Now having said all of this, having more platters even without reading them in parallel can increase drive performance, but it's really a tradeoff. On one hand, having a lot of platters means that (at the same platter density) you don't need to move the actuator as often for track-to-track seeks. Instead, you are doing head switches which are a fair deal cheaper. This results in faster seek times. At the same time though, having a lot of platters means that your actuator arm is bigger, and thus heavier. Having a heavy actuator arm means that you can't move it as fast, and thus your seek times suffer. Similarly, having a lot of platters means that it'll take a larger motor to spin them the same speed as it would for fewer platters, and thus your drive is going to be larger and produce more heat and noise at the same RPM.
In the end, it probably makes sense to use a limited multi-platter approach (maybe 2-4 platters), but keep RPM and platter density high. Additionally, unless you are talking about the really highend (say 15k RPM drives), it's currently more economical to raise the platter density and spindle speed rather than going for multiple actuators, as both approaches give an increase in bandwidth. There is also always the option of doing multi-disk raids if you need more bandwidth as well.
Nite_Hawk
