thanks for all the suggestions!!!

in regards to some comments:

b32 v b16 -- a b32 encoding would give me exactly what i wanted, a 16 is entirely doable giving me more than i need with a third level, but a 32 would give me exactly what i want in 2 levels of the structure. now i get to debate if its worth it or not through benchmarking.

fs choice -- i want this to be portable. i dont want to be in the situation where performance is degraded because i have to install this application on a specific filesystem for whatever reason -- and with reiserfs i'd be limited to linux and wouldnt be able to use bsd (although i think it might be supported under netbsd now)