When you have thousands or millions of files in a single directory, there can be drawbacks.
A strategy is to avoid that situation is to distribute the files into sub-folders whose name is for instance the first few letters of the filename, or the first few letters of the filename's hash. That allows the file to be easily findable, while having no more than n files per folder. Example:
/abcdef /fewrof /abcdea ...
/ab/cd/abcdef /fe/wr/fewrof /ab/cd/abcdea ...
This is a very frequently used technique. Is there an English name for it? If not, what is the nearest word or expression that encompasses it?