iDefrag, by Coriolis Systems Limited
Posted: 16-Mar-2007

4 1/2 out of 5 Mice

Vendor: Coriolis Systems Limited Type: SHAREWARE

Reviewer: Mike Lloyd Class: PRODUCTIVITY
$30   Download

Your computer has slowed down over time, and it's starting to bug you. You've done the obvious and purchased more memory, yet you still find the system is got an "old" sluggish feel to it. Another reason for this slowdown that you make have not considered is a poorly fragmented hard disk. Fragmentation comes in two flavors: single files split into pieces scattered on different physical locations of the hard drive, or related files that may be contiguous on your drive, but if these are system files, the system is essentially fragmented since it has to use these programs for bootup and normal operation. Typical defragmentation programs do not check for this latter type of fragmentation since the files themselves may not be fragmented. The end result of fragmentation is that it takes your machine longer to start up, it takes programs longer to start, and above all, it takes longer to get your work done.

Fragmentation occurs when your files, or groups of files, are simply to large to fit into a free contiguous block of space on your hard drive. The file system has to split them up and move them wherever it can find room, and then keep track of their locations. When the files are in use, the file system is jumping all over the hard drive to load the data into memory.

The solution is to defragment your disk with a tool such as Coriolis Systems' iDefrag. iDefrag is a program that defragments and optimizes the data stored on a disc volume or disk images. Defragmenting your disk volumes increases the performance of your hard disk and file system, and defragmenting your disk images prior to burning them to CD/DVD increases the performance of the CD or DVD once it is burned. iDefrag also provides detailed information concerning the underlying structure of a volume's file structure.


  • Supports Panther and Tiger file systems
  • Email notifications or audible signals when done
  • Supports HFS and HFS+
  • Supports case sensitive and journaled file systems
  • Supports adaptive hot file clustering ("Hot Zone").
  • Four powerful defragmentation algorithms:
    • Compact data, moving all free space to one place
    • Optimize file system metadata
    • On-line defragmentation (while disk is mounted)
    • Advanced programmable optimization
  • Rearrange your disk the way you want
  • B-Tree metadata file compaction/optimization support
  • Thermal monitoring to make sure your disk doesn't overheat
  • High performance user-defined file classification engine
  • Per-block and accurate whole disk display
  • Detailed statistics so you know whether you need to optimize
  • Inspector allows you to view details of individual extents/files
  • Quickly jump to specific files to examine them in more detail
  • Altivec accelerated display for improved performance
  • Auto-update feature
  • AppleScript support


  • Mac OS X 10.3.7 - 10.4,
  • 450MHz PowerPC or better with 512MB RAM

Review Configuration
The machine used to review this product consisted of a 17" G4 iMac with 768 Mbytes of memory, an internal 80 Gbyte hard drive, a 200 Gbyte drive connected using Firewire 1394a, a 300 Gbyte drive connected using Firewire 1394a and running Mac OS x 10.4.


Open the CD or disk image and drag and labeled "iDefrag" into the Applications folder on your hard drive. The help file provided with the application contains instructions to create a bootable CD to use the defragmentation algorithms that cannot be performed on the startup disk. The developers also provide a program that creates a bootable image that can be burned to a CD.

When iDefrag was first released, the developers recommended that "iDefrag" be run from a hard drive due to the lack of virtual memory when booting from a CD (this could lead to failures due to exceeding the available memory to support the defragmentation process). However, they have recently changed their advice. Due to improvements in iDefrag, memory usage has been minimized, so any Mac with 512MB of RAM or more (which is most new Macs) can run from the CD. Running from CD has the advantage that iDefrag is in control of the execution environment, avoiding dismount problems due to Spotlight as well as guaranteeing that no system hacks are running.

In Use
iDefrag is simple to use. If you are only going to use the quick (online) optimization (files only) option, you simply launch iDefrag, select the volume to optimize and click on the "Go" button at the top of the window. Even the "startup" volume can be optimized using this option.

For the other defragmentation options, the "startup" volume cannot be optimized. If you want to perform the other optimizations on the current "startup" volume, the "startup" volume must be changed and iDefrag started from a different startup volume (either on a different hard drive or from CD).

The optimization process typically takes a long time, particularly if the volume is highly defragmented. Since performing a "Full Defrag" from the beginning seems to take longer and if the "startup" volume is being processed, my machine is unavailable. iDefrag provides options to give you an audible signal when the process is done, or if you are going to be on another machine, you can even have an email notification sent to you.

Defragmentation in Process

I generally perform a "Quick" optimization while the machine is in use followed by a "Full Defrag". This approach seems to take an overall shorter period of time, while dramatically improving the overall availability of the machine. While the "Quick" optimization consumes system resources, it does not adverse impact the system's usability while it is running. Note that the developers warn that the software attempts to protect the system's state during optimization, an unexpected failure (e.g., kernel panic) caused by other software could damage the volume's structure.

Multiple Optimization Algorithms
iDefrag offers a number of features that support the optimization of a system's hard drive, and it supports five different optimization algorithms. Compact moves all of the files to the beginning of the volume and is useful to consolidate the volume prior to repartitioning it. Metadata works with the volume metadata and the adaptive hot zone system. The volume metadata data is moved to the metadata zone or to the start of the volume and defragmented. Hot files are moved to the metadata zone and other files are removed. All files that do not exist on the volume are removed from the hot file B-tree. Optimize runs iDefrag's optimization routine and rearranges the files according to the selected class set. This allows the user to optimize files according to their attributes, such as name or size. Full Defrag runs the Metadata algorithm followed by the Optimize algorithm. Once this is completed, if the options are set, the B-Tree files are rebuilt. The Quick (online) algorithm attempts to defragment fragmented files without dismounting the volume, which is limited to ordinary files that have no hard links. This ability to optimize files while the volume is still mounted is unique among the tools that I have used.

Adaptive Hot Zone
Apple discourages defragmentation of hard drives, since the process can destroy the structure of the adaptive hot zone area on a volume. By modifying this area, system performance can be adversely affected by the optimization process. This is true if it is moving files into or out of the area with no regard to their "hot zone" membership. iDefrag preserves the structure of the "adaptive hot zone", thus avoiding any such performance impacts. The developers state that iDefrag is unique in its awareness of the "hot zone".

Detailed Graphical Information
iDefrag provides detailed information of the current state of the hard drive, which is updated during the defragmentation process. The Layout tabs shows detailed information regarding the defragmentation process.

Layout of Defragmentation in Process

The bottom of the window shows the overall structure of the disk volume, color coded to indicate how things are being grouped.

Color-Coded Progress of Defragmentation

This bottom display also shows a set of green triangles that mark the location that the blocks are being moved from. The red triangles show the location where the data is being written. The black triangles represent the area that is being displayed on the large detailed window above. To see what each of the colors mean, you can open up a "Key" window for a list of all the colors and their associated names. There are so many colors that some of the colors end up being difficult to tell from the others (e.g., "Fragmented" is very close to "Group Quota File", "Journal" is very close to "Hot Files B-Tree", etc.). An undocumented feature, you can click on the color chips to change the color and make them more distinct. With so many keys, however, it may be difficult to find better color choices (which is probably why the default colors are as they are).

Color-coded Key

Using the "Files" tab, you can also see a list of the most fragmented files on the volume. It shows the number of fragments, and includes information about the file, such as the ID, size, name, and path. Surprisingly missing from the file information is the class of the file.

Most Fragmented Files

Using the "Statistics" tab, you can view the overall volume statistics, such as the number of fragmented files and the directory fragmentation.

Defragmentation Statistics

Optimizes Disk Images
iDefrag can defragment disk images, a rare feature of defragmentation software. By doing this, you can enhance the performance and reliability of the CD or DVD being burned with the image.

All of the iDefrag's documentation is provided through the application's help system. I found it informative and well organized. Its architecture is hierarchical, and, where needed, tied specifically to features of the program. There are a few minor things that are not discussed in the documentation. For instance, side drawers open on the side where there is room (in the documentation it is depicted on the left side, but in my tests it opened on the right side). I was unaware that clicking on the color chips allowed you to change the colors, and this is not mentioned either. Aside from these very minor exclusions, there appeared to be no other problems with documentation. In areas that may be controversial, such as the section "Why Defragment?", the developers presented a thorough argument that addresses both sides of the issue. They offered solid rationale for at least occasional volume optimization.

iDefrag is a single task utility for disk defragmentation. It provides outstanding feedback during the volume optimization process and is simple to use. This tool addresses many of the arguments posed against volume optimization, such as preservation of the volume hot zone, and also allows you to defragment disk images so that your burned CDs and DVDs will have better performance. Overall, iDefrag does only one thing, but it does it really well. iDefrag is an excellent tool for critical volume optimization, making it a valuable edition to your Mac toolbox.


  • Allows file defragmentation on startup volume
  • Works with disk images
  • Status displays are detailed and informative, especially during defragmentation
  • Preserves volume "hot zones"


  • Default key coloring is indistinct for some classes
  • File's class not provided in the info window
  • One trick pony

Overall Rating

4 1/2 out of 5 Mice