iDefrag is a disk defragmentor for Mac that is in charge of optimizing the location of files in a predetermined volume.
It consists of five different defragmentation algorithms that allow you to perform the process by following different patterns. The only one of them that can defragment a mounted volume answers to the name of Quick (online).
To use the rest of the algorithms in the boot volume, it is necessary to boot the computer from a different volume. The complete version of iDefrag includes a tool to generate a booting CD/DVD with which to perform this task.
A function denominated Thermal Monitoring supervises the disk temperature at all time. If it is too high, iDefrag will stop defragmentation until the device cools off.

iDefrag for Mac is advanced macOS disk defragmentation and optimization tool. Supports the very latest features of HFS+, including journaling, case sensitive filenames and adaptive hot file clustering (which means it won't mess-up the Hot Zone). iDefrag for macOS helps defragment and optimize your disk for improved performance.
If you use spinning disks, you’ll have noticed that over time it takes longer and longer to access your files, to start your applications and even to start your machine. This is an unavoidable consequence of the way hard disks work. It can be made better or worse by the design of the filesystem (and, actually, in this respect your Mac’s filesystem, HFS+, is one of the best), but in the long run there’s really no way to avoid this effect. The cause of this slow-down is fragmentation, and when it happens, you need this app.
New in iDefrag:
Overhauled, Yosemite-style UI
'We’ve made iDefrag fit in with the latest version of macOS.'
Simpler, easier to understand statistics
'The old statistics tab was dense and hard to understand. We’ve simplified and refined the information, and put it in the sidebar.'
New “Selected Files” algorithm
You can now select multiple files and tell the tool to defragment them all at once.
Better handling of bad blocks
'We’ve improved the way the app deals with bad blocks; it will now tell you which file is affected and carry on with the rest of the disk.'
New documentation
We’ve rewritten the documentation to make it easier to read.
Improved support for Retina displays
The program will look even better on that new 5K iMac…
Features and Highlights
iDefrag is not just a defragmenter
It’s a disk optimizer. That means it doesn’t just defragment individual files — it actually rearranges the files on your disk so that your system runs faster.
Works on Yosemite
The app works on Yosemite or later. Older systems need iDefrag 2 instead. If you buy iDefrag, you will have access to older versions as required.
No CD/DVD or external disk required!
In most cases you will not need a bootable CD, DVD or another disk to use this product.
Proper support for HFS+
The tool supports journaled and case-sensitive HFS+, and knows about features like the Hot Zone.
Defragment while the disk is in use
The app can perform simple defragmentation while the disk is still in use. Good for situations where you don’t need the full power of the optimizer, but have a few fragmented files you want to sort out.
Beautiful, accurate display
See the individual blocks used by your files, watch iDe frag move them around in real time, and get an at-a-glance overview of the state of your disk.
Note: This application has been discontinued.