For performance in the good-old-days you would use a separate spindle or set of spindles for each allocation. Of course you would group some smaller files but that de-tunes...
I work with Tivoli Storage Manager (TSM). Been working with it since it was called ADSM (V2.1). Antiquated? Maybe. But quite current in how it works...
I like the Shogun technique: to make my best estimate and then to multiply it by a factor. (Yes in Shogun it was gifts/rewards and the multiplier was progressively...