Do I need to defragment Mac OS X?
I think the best answer for this comes straight from this apple support KB
About optimization and fragmentation
Disk optimization is a process in which the physical locations of files on a volume are "streamlined." Files and metadata are re-arranged in order to improve data access times and minimize time moving a hard drive's head.
Files can become "fragmented" over time as they are changed and saved and as the volume is filled, with different parts of a single file stored in different locations on a volume. The process of collecting file fragments and putting them "back together" is known as optimization. However, if a failure occurs during optimization, such as power loss, files could become damaged and need to be restored from a backup copy.
Do I need to optimize?
You probably won't need to optimize at all if you use Mac OS X. Here's why:
Hard disk capacity is generally much greater now than a few years ago. With more free space available, the file system doesn't need to fill up every "nook and cranny." Mac OS Extended formatting (HFS Plus) avoids reusing space from deleted files as much as possible, to avoid prematurely filling small areas of recently-freed space.
Mac OS X 10.2 and later includes delayed allocation for Mac OS X Extended-formatted volumes. This allows a number of small allocations to be combined into a single large allocation in one area of the disk.
Fragmentation was often caused by continually appending data to existing files, especially with resource forks. With faster hard drives and better caching, as well as the new application packaging format, many applications simply rewrite the entire file each time. Mac OS X 10.3 Panther can also automatically defragment such slow-growing files. This process is sometimes known as "Hot-File-Adaptive-Clustering."
Aggressive read-ahead and write-behind caching means that minor fragmentation has less effect on perceived system performance.
I suggest also taking a look at Server Fault's answers as well:
- https://serverfault.com/questions/812/do-i-need-to-defrag-macosx-filesystems
- https://serverfault.com/questions/14660/defragmenters-useful-for-nix
My answer on Server fault fits here as well :
It's a bit of a yes, no answer. Useful in certain circumstances but it's less of an issue than it was with FAT or regular HFS. All filesystems will fragment but newer ones are more resistant to fragmenting so badly.
Speaking for Mac OS X specifically HFS+ does a decent enough job of trying to keep things from being fragmented compared to older systems but it still happens just not on the same scale. The OS itself also defrags "small" (20MB or smaller) files on the fly since 10.3 (Panther).
Fragmenting still happens and you can see performance drop because of it, especially in video editing systems or a workflow that requires the ability to read or write large files quickly to the disk. For your standard user - a near non-issue.
The most popular options for defragmenting a hard drive for OS X I've used and run across are:
Cloning the hard drive to another drive and back. This is done using Carbon Copy Cloner or SuperDuper and requires an extra hard drive. If done as part of a backup routine the time hit may not be terrible but it's free to do it this way.
iDefrag, Drive Genius and a handful of other utilities will all defragment your hard drive as well. Personally I prefer iDefrag.
It's not that OS X doesn't need to be defragmented. It's that like Windows Vista and Windows 7, OS X automatically defragments your drive in the background when the computer is idle. You shouldn't ever need to manually defragment your drive in OS X.