 The HFS Plus file system transparently defragments files that are less than 20 MiB in size and are broken into 8 or more fragments, when the file is being opened.The now obsolete Commodore Amiga Smart File System (SFS) defragmented itself while the filesystem was in use.The defragmentation process is almost completely stateless (apart from the location it is working on), so that it can be stopped and started instantly.