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gulmatan · 05:41 PM

Hi all,

I have an external 250GB HD that's had its long history of files shuffling in, out around. Is it advisable to defrag this drive using an app such as TechTool Pro? Also, are there better/other utils than TechTool Pro to do the defrag with?

Chuckit · Sep 20, 2007, 05:43 PM

I think defragging is usually a bad idea. In the best case, you might get a minor speedup (though OS X automatically defragments many files anyway). In the worst case, you ruin your disk. In the average case, it probably doesn't do anything but waste time and wear out your disk. The cost-benefit analysis doesn't seem to work out in favor of defragging.

peeb · Sep 20, 2007, 05:44 PM

OSX defrags somewhat automatically - leave it alone. Is there some reason why you think it needs defragging?

gulmatan · Sep 20, 2007, 07:41 PM

Originally Posted by peeb

OSX defrags somewhat automatically - leave it alone. Is there some reason why you think it needs defragging?

Okay on point 1 but, what does OS/X do for and with maintaining external drives?

On point 2, I've downloaded so many Podcasts that, when iTunes updates/loads new Podcasts, I've run out of room and my Ext HD is full. I've gone through this routine of repeatedly letting my Ext HD fill up with Podcasts and then I remove the duplicated Podcasts. So, I surmise that quite a bit of fragmentation might be happening.

peeb · Sep 20, 2007, 07:43 PM

OSX automatically defrags any file over 20mbs when it encounters it and has spare time. You do not need to defrag in the normal course of events, indeed, it can hinder performance. OSX deals with disk optimization on it's own. Unless it is malfunctioning, you do not need to get involved. Is there some reason you think things are not running well?

reader50 · Sep 20, 2007, 09:16 PM

I'm afraid the above info is incorrect. OSX defrags files under 20 MB in the background. Larger files are ignored. There are additional limitations, for example the HD must have a certain amount of free space left. And I've yet to hear for sure that OSX does anything to non-boot drives.

iDefrag is the best defragger. You can read their additional info page for more defrag explanations. Regularly running an HD up to 100% full is a textbook case for someone who needs to defrag. Heavily fragmented disks not only have access delays, they tend to be more prone to directory damage, and harder for utilities to fix.

Note: always repair a disk before defragging. At the very least, run Disk Utility across it to confirm the filesystem is clean.

Chuckit · Sep 20, 2007, 09:24 PM

Note that you need to back up before you defrag, because it can hose your disk. Also note that if you've just backed up, you can more simply wipe the disk and restore from backup rather than defrag it.

imitchellg5 · Sep 20, 2007, 10:31 PM

I've used a defragger a few times and at the worst it's had to defrag 7 files on 120 Gb of data. Not really worth the time, in my opinion.

AC Rempt · Sep 21, 2007, 01:26 AM

Back in the day, I would defrag once a month along with all the other good practices like backing up, rebuilding the desktop cleaning out useless files to save space, etc. Now, I back up once a month, and everything seems to be running just fine. OS X is really, really stable for me, and it has been since 10.1, so I really don't worry about maintenance the way I used to.

Looking back, I'm not sure there was any real noticeable benefit from defragging. After I'd do it, the machine never felt any faster, though all the pretty graphics showing how the files were now all lined up together made me happy.

CharlesS · Sep 21, 2007, 01:32 AM

Originally Posted by reader50

Regularly running an HD up to 100% full is a textbook case for someone who needs to defrag.

Regularly running a hard drive up to 100% full is a textbook case for someone who needs to get a larger hard drive.

It's been my experience that running an HFS+ disk nearly full for an extended period of time tends to cause a lot more than just fragmentation - it tends to cause directory damage, including overlapped files, which result in data loss that no disk utility will be able to recover. Plus, most defraggers that I've used require you to have a certain amount of free hard disk space anyway in order to do their thing, so I'd say that what you need in such a case is not a defragger - it's a larger hard drive.