Not SSDs. You can run samples (read only) at as close to full as you want. If total transfer time is a limitation, you are better off using multiple smaller SSDs, using hard links between them to split heavy use libraries.
With HDDs, if you only need half the drive for your samples, you are better off formatting the first partition just a little bigger than that required for the libraries.
This is called ‘short-stroking’ because it limits the maximum head travel time, which can allow lower latencies. Of course, what is in the other partition(s) on the drive MUST NOT be used with the samples, otherwise it forces a minimum head travel time.