Technically those are files, but because they are used to store volume metadata the builtin file move code has trouble moving them on a live (mounted) partition, but defrag utilities that work on the disk offline can just move them to the beginning of the partition, which allows the volume resizer to work. The reason is that those failures are largely caused by some core structure of the volume (Like the extents or catalog file) existing in blocks outside the target layout. The only time it is generally worthwhile to defrag an OS X drive is when you are trying to do an LVM operation (like shrink a partition for bootcamp), and the builtin tools fail.

Unless you do something really odd (constantly keep the drive over 99% full while doing lots of reads and deletes) it is very hard to significantly fragment the drive. While it is possible to fragment it, the implementation in the OS X kernel includes a number of features that tend to limit fragmentation, including deferred block allocation and hot banding. Generally speaking, you do not need to defrag HFS+.

I myself had an issue similar to the one described in mozillla's issue tracker. I know that web browsers (the field I'm interested in) are at least sometimes are affected by fragmentation (ex.: mozilla, chrome). I have sampled too few a volume to generalize my 'results'. Note that I do not intend to make any claims regarding the fragmentation-resistance of HFS+.

There's no easy way to tell if your specific problem is caused by fragmentation.īTW answer), the cited Fragmentation in HFS Plus Volumes explicitly says this:.

Some people do have issues caused by fragmentation ( 1, 2).

There's no built-in or free and popular defragmenter utility for Mac OS X (although there are commercial ones).

'If your disks are almost full, and you often modify or create large files')

Apple believes these features are enough to spare the majority of their users from caring about fragmentation issues, but also says you ''might'' benefit from defragmenting in some cases (e.g.

There are features in Mac OS X designed to prevent some of fragmentation.

It's somewhat true: since there's nothing you can do about it without spending $20 on something that might not improve the performance of your computer at all, you could instead focus on other maintenance tasks and just buy a shiny new mac (or reinstall) when the old one gets too slow.īut: An important prerequisite for not caring about disk fragmentation is always keeping some free space on your disk (I couldn't find any recommendation not pulled out of thin air, but 20% is often mentioned). Most people will tell you Macs don't suffer from disk fragmentation, citing technical arguments most people don't understand.

How do you defrag an imac