This entry was published at least two years ago (originally posted on October 29, 2003). Since that time the information may have become outdated or my beliefs may have changed (in general, assume a more open and liberal current viewpoint). A fuller disclaimer is available.
I have no idea whether or not this is a standard feature in other Unix systems, but it appears that there’s a very handy little “under-the-radar” feature in Mac OS X 10.3/Panther — automatic file defragmentation.
Everytime an application opens a file for reading, HFS+ checks if the file is fragmented and is less than 20MB in size. If so, it copies the file’s contents to a continuous region on the disk and frees up the previously allocated blocks.
What a wonderfully convenient feature. Even nicer, when someone asked if there were any official confirmation from Apple about the feature, someone else posted the source code from the Darwin (command-line only open source) version of the core system.
(via MacSlash)
This is a standard UNIX thing: you don’t worry about fragmentation on UNIX-based systems (those based on UFS or FFS). It’s generally in the 1-2% range.