Manual:FSFileBackend.php/en

FSFileBackend, which extends, is the class for a file system (FS) based file backend. All "containers" each map to a directory under the backend's base directory. For backwards-compatibility, some container paths can be set to custom paths. The wiki ID will not be used in any custom paths, so this should be avoided. Having directories with thousands of files will diminish performance. Sharding can be accomplished by using FileRepo-style hash paths.