One billion files on Linux

The advantage of putting all files in the same directory is that it's slightly easier to code it that way. The disadvantage is that you have directories that effectively can't have their content listed using ls, you likely can't even count the number of files in the directory. Basically some kind of storage tar pit. I think I'll stick to using subfolders. And once mailing lists with more than say 10 million messages in them become common, I'll start worrying about a subfoldered replacement for maildir. :-)