My Rails app uses memcache for fragment, action and other caching but has a long tail of infrequently accessed items so its hard to keep them all in the cache without making it really huge and gobbling up dozens of gigs of server memory. But my caching servers do have hundreds of gigs of free disk memory that is unutilized, as do my app servers. So I was wondering if there something like memcache that is disk backed - a two stage cache using disk for virtually unlimited long term storage, and a smaller amount of memory for frequently accessed items.
I realize I could do this programatically, indeed I've implement something like it myself for some limited cache uses, but if there is already a Rails plugin or memcache like replacement using that would be better than reinventing the wheel.