[paulinbognor]

Hi All
Still waiting for my Mac Pro to turn up and getting everything sorted before it arrives.

I have read a lot of things about the fact that you don't need to defragment Mac HD. In theory this sounds great but I wanted to double check that this is the case. I'm currently PC based using NTFS formatted HDs on Win XP. I defrag my two main drives every 72 hours and in an average 72 hours there are usually 1500-5000 fragments in files.

So will I just not get the same amount of fragments when working on my Mac Pro? Or is the 'you don't need to defrag' advice aimed at general home users?

Thanks in advance

[TETENAL]

Mac OS X automatically defragments files smaller than 20 MB. For larger files it is practically irrelevant. Your hard disk can read a movie file fast enough to play the movie without problems whether it fragmented or not.

[Tomchu]

Originally Posted by TETENAL 

Mac OS X automatically defragments files smaller than 20 MB. For larger files it is practically irrelevant. Your hard disk can read a movie file fast enough to play the movie without problems whether it fragmented or not.

Mmm ...

I can think of a million reasons why that's not a good thing to say, but I'll leave it with this: Just because something works one way, doesn't mean it couldn't work better.

[Chuckit]

In most cases, defragging on the Mac is a waste of time. More importantly, most defragging software seems to be unnecessarily dangerous — if it gets interrupted in the middle of operating, your disk can be totally hosed. There are a few cases where defragmenting can be useful, but I don't know many Mac users who have been harmed by not defragging.

[mac128k-1984]

Originally Posted by Tomchu 

Mmm ...

I can think of a million reasons why that's not a good thing to say, but I'll leave it with this: Just because something works one way, doesn't mean it couldn't work better.

Well here's apple's stance on it KB Article and you'll see that in most cases it could actually degrade performance.

[chabig]

Originally Posted by Tomchu 

Just because something works one way, doesn't mean it couldn't work better.

Media streams need data a certain bitrate. If the drive can provide the data at the required rate, then it can't work better--no matter how the data is physically arranged on the platters.

[Catfish_Man]

Originally Posted by chabig 

Media streams need data a certain bitrate. If the drive can provide the data at the required rate, then it can't work better--no matter how the data is physically arranged on the platters.

Unless other applications are also touching the disk, in which case it could degrade their performance (spending more time seeking, less time free for other apps).

[Sourbook]

I have never defragged since I OSXed. I do however rebuild my directory with DiskWarrior after a system update. I don't know if it helps at all, but it does make me feel better.

[TETENAL]

Originally Posted by Catfish_Man 

Unless other applications are also touching the disk, in which case it could degrade their performance (spending more time seeking, less time free for other apps).

If other apps are accessing other files, then you have head movement anyway. Whether the different files are defragged or not.

If it makes you "feel better" then by all means do it. Life's too short to feel bad. But be aware that defragging is a cargo cult.

[Tomchu]

Recording raw video. Fragmented free space. 'Nuff said.

And comments like this: "If other apps are accessing other files, then you have head movement anyway. Whether the different files are defragged or not" demonstrate a lack of knowledge about things like buffers and read-ahead.

[Chuckit]

Originally Posted by Tomchu 

Recording raw video. Fragmented free space. 'Nuff said.

You just named the one case that I'm aware of where defragging can have any benefit, and you don't need any special tools for defragging in that case — just erase and restore. (I mean, assuming you weren't trying to record to your boot drive and expecting peak performance.)

[tooki]

See TidBITS: Optimizing Disks Is a Waste of Time

tooki

[Catfish_Man]

Originally Posted by TETENAL 

If other apps are accessing other files, then you have head movement anyway. Whether the different files are defragged or not.

If it makes you "feel better" then by all means do it. Life's too short to feel bad. But be aware that defragging is a cargo cult.

I agree with you overall (haven't even seen a defragging tool in over a year). However, seeking twice is slower than seeking once. In a timeslicing system, if more time is used for one thing, less is available for others. It's not a big deal at all unless there's very severe fragmentation (unlikely) or extremely high sequential bandwidth requirements, but it is the case.

[larrinski]

Another good reason to switch to the Mac. No need to defrag...

[paulinbognor]

Thanks all for your replies.

I guess i'm going to have to just run the system for a week or two and see what happens. 70% of my work is done in large photoshop files (50-400MBs).

Is there a way of checking how fragmented a drive is on a Mac so that I can see how it copes and then act accordingly?

[monkeybrain]

I've never defragged any of my Macs. However, last week I tried to install Boot camp on my Macbook, and because I had only about 10 GB left on the disk (now up to 17 GB) the boot camp installer would not work. It seems the problem is not exactly the space, but where that space is because boot camp is creating a second partition, thus you need a large, empty, and continuous chunk of space. The only way for me to install boot camp now is to defrag or wipe clean and reinstall.

With boot camp becoming part of Leopard, and the ability to change partition size on the fly like that, I can foresee it becoming a more common issue.

This app: Coriolis Systems :: Products :: iDefrag will defrag your drive, and you don't need to buy it just to look at the fragmentation (seems I have some files from OS 9 days, must be over 5 years old, that are badly fragmented).

[jasong]

Yeah, and if those files are under 20MB, you simply have to open them and OS X will automatically defragment them.

How's this for proof you don't need to defrag OS X, defragment isn't in the built-in OS X dictionary ;-)

[mduell]

Originally Posted by chabig 

Media streams need data a certain bitrate. If the drive can provide the data at the required rate, then it can't work better--no matter how the data is physically arranged on the platters.

Assume a hard drive has a read rate of 100MBps and a seek time of 10ms (numbers to make the math easy, on the same order of magnitude as reality).

Playing a contiguous 10MBps media file is trivial since there is (almost) no seeking and plenty of bandwidth.
Now consider a 10MBps media file that has 64KB per fragment; in 11ms you get 64KB, or 5.7MBps, falling well short of the 10MBps requirement for smooth playback.

As you can see in this example, the drive can provide data at the required rate, but due to the physical arrangement of data on the platters it is unable to.

[monarch]

Hi All,

I just wanted to post in this old thread to share a recent experience I had with defragging my iMac (24" core 2 duo).

I was experiencing increasing slowness for weeks - spinning beach balls even when all I had open were Mail and Firefox. It was rough and I was frustrated. I tried everything else to fix this - I used onyx to clear my system and application caches, repaired my disk permissions, nothing helped.

Then, I downloaded a defrag tool and found that my drive was really fragmented. Not my files, mind you. But the free space on my drive. While OS X does have built in file defragmenting, it does not automatically defragment the free space on your drive.

After I ran the defrag program and consolidated the free space on my drive, this solved my problems. No more spinning beach balls and my iMac runs FAST.

I suspect all of this fragmented free space is a result of my using my iMac as a personal DVR with my eyeTV. I record a lot of TV shows and edit them - I suspect this contributes greatly to the free space on my drive getting fragmented all over the place.

Anyway, if your iMac is painfully slow and nothing else helps, give this a try. It worked for me.

Cheers.

[Chuckit]

I still do not recommend using a defrag tool. If you want to defragment a drive, back up and restore. Because defragging can hose the drive, so you need to back up anyway.