HFS+ Fragmentation 

Remember the days when we use to defrag our disks with Norton SpeedDisk? When was the last time you defragged under Mac OS X? No need to thanks to Mac OS X built-in measures against fragmentation?

Learn more about the topic by reading Amit Singh's "Fragmentation on HFS+ Volumes" on kernelthread.com.

Defragmentation on HFS+ volumes should not be necessary at all, or worthwhile, in most cases because the system seems to do a very good job of avoiding/countering fragmentation.

It is risky to defragment anyway: What if there's a power glitch? What if the system crashes? What if the defragmenting tool has a bug? What if you inadvertently reboot? In some cases, you could make the situation worse by defragmenting.

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Comments and responses

  • 23 May 2004

    While I am a huge fan of AlSoft’s Disk Warrior (disclaimer: I knew Al and a bunch of his employees) and go to it first to fix things because it’s better and non-destructive (until I tell it to be), I never could bring myself to run PlusOptimizer (AlSoft’s defrag tool) in the real-time continuous optimizer mode he recommended.
    But I’m pretty sure the PlusOptimizer was safe in the listed conditions and was designed to be fail-safe (i.e. if it failed due to a bug, it was supposed to be able to recover, just like his drive fixing utilities.)
    The down side of optimizing was always if you had a corrupt B-tree and two files “owned” the same block and one moved it. I always ran DiskWarrior/Norton/Disk First Aid first, and didn’t optimize unless I was clean.
    But yeah, I appeciate OS X and not needing to defrag for performance reasons.

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