as @haitch has said any old cheap 5400rpm HDD is perfectly fine for mining burst the only time you will see a benefit from a fast HDD is during plotting , if you have a large unused SSD or somthing like an ultrafast 10kRPM HDD use it to plot then transfer the plots to the slower HDD's ..... but no need to purchase any fast drives just use the fastest one you have for plotting and cut paste them to slower drives
