[junkgear]

Basically a hard drive can only read and write so much data at any given time. If everything is running off of the same drive, then the OS is accessing information from it, your sample libraries are accessing information from it and your audio files are being read/written to/from it. That's a lot of data all at one time, so at some point, one or more of those things is put in a line and has to wait before it can be processed. And this is where your system starts to slow down; waiting for all that info to be read/written to the hard drive.

A simple solution to this problem is to separate this data onto separate disks. One for the OS and Pro Tools itself, one for your session (audio) files and one for your sample libraries. In this configuration, the drive only has to serve up any one of these things at a time, which removes the bottleneck and improves system performance.

Now mind you that newer computers are pretty powerful and SSD drives are a lot faster than older mechanical drives, so you can get away with a lot more these days as far a running things from a single drive. Mind you, this all depends on how big your sessions are, how many audio tracks and how many sample based instruments you use. At a minimum, I would suggest a separate drive for your sessions.

The drive you linked would be perfectly fine as your session drive.

Hope that clears it up a bit.