Defragmenting solid-state disks: Good idea, or totally useless?

Disk defragmenting is generally good thing. However, some would argue that depending on the file system and disk access patterns on your rotating media, any performance improvements aren’t worth the effort.

Take the Macintosh, for example. In “Defragmenting your Mac’s hard disk,” updated just yesterday. Apple says that

The file system used on Macintosh computers is designed to work with a certain degree of fragmentation. This is normal and does not significantly affect performance for the majority of users. You should not need to frequently defragment the computer’s hard disk.

In reality, however, the nature of the files, the nature of the work you are doing, the nature of random-access disk mechanisms, and the exact order in which the files are segmented can all have a bearing on the resulting performance. In general, there is not significant degradation of performance from normal use of your computer.

If you create and delete a large number of files, your hard disk may become fragmented to the point that you may see a slight slow-down of file system performance.

I defrag my Macs’ hard drives about every six months or so, or after a major system update (like going from Mac OS X 10.4 Tiger to 10.5 Leopard). The defrag tool that I use is iDefrag, a $34.95 utility from Coriolis Systems.

What about solid-state disks, like the ones in the MacBook Air, or increasingly, in servers? Is defragmenting a good idea? Or is it worthless? Worse, could the intense I/O (and heat) associated with defragging cause undue wear to an SSD?

That’s the topic of a story by Alex Handy, “Do Solid State Disks Need Defragging,” published in the July 15 issue of Systems Management News. Frankly, I’d not thought about the topic before hearing that Alex was working on the piece. I believe you’ll find it interesting to read the discussion and the conclusion.

Z Trek Copyright (c) Alan Zeichick
2 replies
  1. Paul N. Leroux
    Paul N. Leroux says:

    Defragmentation can be a problem, which is why it’s useful to minimize it in the first place. At QNX, for example, we have an embedded transaction file system for NAND flash that reduces fragmentation by consolidating smaller writes into larger write transactions. I’m not sure what Mac/Windows file systems do, however.

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