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Another way of defragmenting a Mac

Friday, November 19th, 2010 by Servage

Defragmentation of a Mac computer always triggers different opinions. In various other discussions online you can find very different opinions on the same question. However, it is a fact that your Mac gets slower over time. It’s annoying, but it happens. It’s nothing unusual. It happens to any other computer as well. Unfortunately it’s not a black & white story with a simple solution. There are many reasons for computers getting slower over time, such as many apps running at the same time, hidden services running in the background, fragmentation of data, maybe even wear on mechanic components, such as hard drive.

The official position from Apple is that defragmentation is not necessary, because the file system basically defragments itself on the fly. This is partly true, because it only applies to certain (most) conditions. So in general your system will fragment slower than other computer systems, but it does still fragment. In a personal subjective test, I found that a 2009 iMac started to get slower and slower. Particularly I more and more often found myself waiting with the rainbow-ball circling, indicating that the system was busy. Obviously it was the hard drive – you could hear it. Running the Activity Monitor app confirmed the I/O load. This was actually surprising me a bit, because actually I didn’t have any weird processes running. Suddenly the Mac just had the need to do something, and spend all it’s (I/O) resources on some secret background stuff. Really annoying, and really stupid, to be honest. I want my computer to serve me, and do “background stuff” when I’m gone… Anyway, to work a little with the problem, I decided to check my disk for fragmentation. For this purpose I downloaded the iDefrag Demo and got a view of my disc. And yes, it was fragmented. Maybe not as much as I thought, but it clearly was. The statistics show 2% fragmentation off files, and 85% fragmentation off free space. I guess the system really does defragment in the background somehow – maybe that is even that particular annoying thing that makes the rainbow (of death…) appear so often. Either way, I wanted to test if a defragmentation would help, so I checked the available software. No free stuff, just some quite expensive premium apps that I did not want to throw money after. In my opinion I bought a fine computer. It shouldn’t be necessary to spend money to keep it running… So I looked for another solution and came along some tips suggesting a reformat of the disc followed by a reinstall of the entire system with a Time Machine backup. Since I was already taking backups with Time Machine on a Time Capsule connected via Gigabit Ethernet, that would be no problem.

How to reinstall you Mac with a Time Machine backup

  1. If you do not already have a Time Machine backup, connect an external drive and do it (via System Preferences > Time Machine).
  2. Boot your Mac with the Mac OS install DVD (Put it in your drive. Restart. Hold the “option”-button pressed while booting, until you get a selection showing your drives. Select the install-disc)
  3. Choose language from the menu
  4. Instead of just following the wizzard, now go into the top menu, select the Disc Utility from the dropdown called Tools or Utilities. Use the disc utility to erase your system disc (recommend to zero-out data in security options).
  5. Select Restore from Time Machine from the same dropdown. Find your backup and follow the wizzard.
  6. Your system should boot up like you left it when making the last Time Machine backup. Done!


The whole process took 3 hours. 1 hour for erasing the disc and 2 hours to restore the Time Machine backup. This was much faster for my 750 GB disc than a friend of mine spent to defrag with iDefrag on his 300 GB disc (6 hours). Afterwards I checked the fragmentation with the iDefrag demo, and I now had 0% fragmentation, and could instantly feel a performance boost. I have now used the system for a few days after the reinstall, and have noticed fewer appearances of the annoying rainbow balls appearing. It does, however, not feel like a completely “fresh” install of Mac OS. But the comfort of having my known environment is much more important to me, than doing a complete reinstall of the operating system.

I hope this may help some people out there seeking tips on how the improve the I/O performance on their Macs.

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2 comments (leave a comment)

Why would you want to do this?

You could consider this is your Mac shows problems caused by fragmentation. Typical signal is: Often experience slow system due to I/O load at “random” times.

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