if you want to use 3 characters, I would suggest doing directories like /a/aa/aac /g/ga/gab which gives you only 26 directories (more if you do numbers or capitalization) per level... much easier to look at as a human :) that is a pretty common practice, and it is pretty easy to do... it should also keep you pretty well separated, unless your files will have a tendancy toward the same name... then you might want some kind of hashing function, like length of filename plus first and last letter, or something else like that... for randomly distributed filenames, I'd say this /a/an/ant is fine... though I would only create the dirs as they were needed... that way you don't have to have extras like zxq sittig around eating up inodes...

                - Ant