These big drives come with really fast transfer speed, that LMCE doesn't really use. 750GB drives push something like 375MBps, though the SATA interface gives maybe 300MBps tops, probably more like 250MBps. But the highest bandwidth, video, plays at something like <1.5MBps. If those drives could burst transfer when content is requested from them, they'd have a lot of time to spin down between requests. A whole DVD is only max 4.7GB, so a $65 16GB USB Flash drive could cache 3.4 entire DVDs (probably more than 4 movies). But USB does max 60MBps, though multiple parallel USB (on motherboards supporting truly parallel USB, with full bandwidth for each of maybe 4 USB ports) would argue for 4 $15 GB drives to get 240MBps. Since the movies take hours to play, that could be something like 20-30 seconds bursting the requested movie to Flash, for each hour or two pulling them from the Flash. Those Flash drives can probably also cache the entire LMCE from the disk in just 8-10GB of the 16GB cache. The drives might spend something like 90% of the time spun down, even during heavy use, except when skipping through the actual content of a lot of different titles.
How to structure the storage to put a bank of USB Flash drives in the data path as cache for the hard drives, and set the drives to spin down as part of this power saving profile?