The performance gain from a large cache with torrenting is negligible at best. With NCQ alone (on supporting drives) the performance is usually high enough that unless you're transferring significantly faster than your cache size you won't actually see the cache get big. When the typical user has a cache that large, they're trying to deal with an excessive number of torrents (even people with 100mbit symmetric connections). If you're trying to save your drive, having it used little enough that it spins down is worse for it than running it ragged. It's the reason I turned off the intellipark function on my 4 WD greens in my fileserver (it would head-park after 8s of idle by default). The ONLY reason to have any amount of increased disk cache is performance. With platter drives, there really is no such thing as "unnecessary read" because you're keeping your drive from spinning down.