The question whether you need to defragment seemed to be answered by Apple in the technical document that describes the capability of Mac OS X to defragment files itself. It turns out OS X only does this for files that are smaller than 20 MB. Although the technical document says it’s barely ever needed, it does include a sentence on the need for defragmentation when you’re using iMovie –and by extension Final Cut and other Pro applications. These days we all create video files of well over 100 MB and even photos can easily grow beyond the 20 MB file size. Enter iDefrag 2, a dedicated utility that can defragment your drive and files without having to start up from a CD or DVD.
Coriolis Systems is the British developer of iDefrag 2. Unique about their defragmentation product is that it is entirely dedicated to defragmentation. It is fast, reliable, and can defragment startup volumes without having to start the defragmentation process from a DVD or CD.
iDefrag has five algorithms to defragment a disk: full defragmentation, a compacting algorithm that only defragments the free space on your disk, a Quick mode that only defragments files you’re not using, an optimisation algorithm, and a metadata mode. The Full Defrag algorithm defragments files and metadata and repositions files for an optimum result.
The optimization algorithm rearranges files on the disk under the control of a selected class set. This algorithm does not compact or rebuild the B-Tree files like the Metadata algorithm does. The latter method focuses on the volume metadata and the adaptive hot file clustering system. iDefrag will move volume metadata into the metadata zone (if present), or to the start of the volume and defragment it. This algorithm also removes files that are no longer on the disk from the hot files B-Tree.
Unlike other defragmentation products, iDefrag works in the background. However, this is mostly theory on a Mac Mini, because the defragmentation process requires a good deal of memory that is not available to your frontmost application. Furthermore, you risk crashing your system, and a system crash during defragmentation could result in disk corruption.
You can pause defragmentation. iDefrag will then stop what it is doing so that it does not consume any processing power, but if you are using one of the off-line algorithms (such as the full defrag mode), you won’t be able to access the volume (iDefrag has to prevent modification of the volume so that it can resume).
If you stop defragmentation mid-way through, your disk will be left in a useable state, albeit one where iDefrag has only half completed its job. If you were to run the process again immediately, iDefrag would continue from where it had left off.
The iDefrag interface is very easy to use, but has one drop-down menu which I am sure many people will find intriguing: the Class Set menu. Class Sets are the mechanism by which iDefrag decides which files may be moved and provide additional control over the behavior of the Optimize algorithm. A large number of file classes are built-in into the Default Class Set and should not be changed but if you want, you can create your own Class Sets. The reason why you would like to do this is for example when an application depends on the location of invisible license files it dumps in specific invisible folders.
However, most license methods will be covered already by the built-in Class Set –in short: there’s little reason to go about and create a new one. That’s a good thing, as creating these Class Set definition files is not for the fainthearted…
Now for the tests. I used three disks. One was a startup volume that had little fragmentation reported by iDefrag, the other one was a data disk with considerable fragmentation, and the third was my Mac Mini startup disk which showed roughly 12% overall fragmentation (free space and files combined –free space was worse).
I tried iDefrag on the first test disk by using its new startup mode that doesn’t require a DVD or CD. The process involved restarting the Mac in something that closely resembled Safe Boot and then let iDefrag perfrom its magic. It worked and it worked well. The disk got defragmented in under 15 minutes.
The data disk of course proved to be not a problem. I ran a full defrag on a volume that had over 300 GB of file data sitting on it. This took half a day, but at the end the results were fine. This disk did feel snappier, but I really can’t tell if it was faster indeed.
I can tell the Mac Mini running faster after giving that one a full defragmentation, though. The first startup after using iDefrag actually took more time than usually, but every subsequent startup sequence was its usual, fast self. Applications on this startup disk were definitely faster to launch –measurably so– although not all of them were equally faster. Data was read faster too, and this I could especially notice with video and audio files.
Conclusion: a defragmentation application is not really needed on Mac OS X, but it sure speeds up your disk, no matter how big it may be and certainly if you’re running video and audio applications. iDefrag costs 22.00 Euros. For that price you can keep your disks in “optima forma”.