I've had my Dual 1.25Ghz G4 tower for almost 2 years now, and I've never defraged the hard drive. The computer has definetaly slowed down since it was brand new.

In windows, defragmenting the hard drive is built into the operating system. How can I defragment the hard drive on my mac?

Thanks

[jondaapplegeek]

I thought I heard that the Mac System defrags while in use, without the user knowing. I don't understand how it all works, or if this is correct, but if that is not true, I would also be interested how to do this...

[chucker]

Originally Posted by macsforever The computer has definetaly slowed down since it was brand new.

Well, make sure that:
1) you have at least 30% space free on each partition of every hard drive you're using.
2) you frequently clean out caches. Apps like MainMenu will aid you with this.

How can I defragment the hard drive on my mac?

The short answer is: you don't need to. In fact, it is likely to cause more harm than good.

The longer answer can be researched here. Quoting from its conclusion:

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.

Originally Posted by chucker Well, make sure that: 1) you have at least 30% space free on each partition of every hard drive you're using. 2) you frequently clean out caches. Apps like MainMenu will aid you with this. The short answer is: you don't need to. In fact, it is likely to cause more harm than good. The longer answer can be researched here. Quoting from its conclusion:

30% free disk space? My computer came with a 80GB hard drive!!!!!!! I can't keep it 30% empty. It has like 7GB available. Oh well, I guess i'll have to transfer alot of my stuff to my external hard drives.

Thanks. That could have been the main issue.

[chucker]

Originally Posted by macsforever 30% free disk space? My computer came with a 80GB hard drive!!!!!!!

Yes, and if it had come with a 100 GB hard drive, that would be 30 GB. Nonetheless, it is the rough threshold of HFS+ operating at its highest efficiency. It needs room to breathe.

I can't keep it 30% empty. It has like 7GB available. Oh well, I guess i'll have to transfer alot of my stuff to my external hard drives.

Hard drives are cheap. Performance is valuable. The choice is yours to make.

[Kickaha]

HFS+, the filesystem under MacOS X, defragments all files under 20MB in size, as they are written, on the fly.

Defragmentation is essentially a non-issue except for a very very small number of users who need absolute speed, such as high-end video editors. For them, specialized disk solutions exist and are commonly used.

Bottom line: defragging is the least of your worries.

And chucker... 30%?? Are you serious? No way. I have an 80GB drive I frequently run within a gig of full, with no issues. 5GB is the more than comfort zone, in my experience, and then only for serious VM needs. Heck, make it 10GB if you really want, but I think that's overkill. On an 80GB drive, that's only ~12%. I'm going to have to see some evidence other than just anecdotal for this one, before I believe it.

Cleaning caches is a good place to start, and also make sure your Mac is on overnight once in a while to do some of its automated maintenance. Many log files get cleaned up and cleaned out at 3am.

Remembering to reboot once a month or so isn't a bad idea either.

[chucker]

Originally Posted by Kickaha And chucker... 30%?? Are you serious?

Yeah, I'm serious. I realize it's high, but it works for me. The number comes from an Apple file system engineer whose name eludes me right now (no, not the BFS guy).

No way. I have an 80GB drive I frequently run within a gig of full, with no issues. 5GB is the more than comfort zone, in my experience, and then only for serious VM needs. Heck, make it 10GB if you really want, but I think that's overkill. On an 80GB drive, that's only ~12%. I'm going to have to see some evidence other than just anecdotal for this one, before I believe it.

My experience clearly differs from that, but then, I'm mainly on a 60 GB 5400 RPM laptop drive. Not exactly a performance wonder.

I'll reevaluate when I have my MBP.

Cleaning caches is a good place to start

Quite.

Specifically, /System/Library/Caches, /Library/Caches, ~/Library/Caches, and if you're a heavy Safari user, ~/Library/Safari/Icons. Stuff like that.

Remembering to reboot once a month or so isn't a bad idea either.

Yeah, the OS is so stable that you sometimes forget that it's been running for so long. Rather unusual for a desktop OS.

[Kickaha]

Originally Posted by chucker Yeah, I'm serious. I realize it's high, but it works for me. The number comes from an Apple file system engineer whose name eludes me right now (no, not the BFS guy).

I'd love to see the reference, if you can find it. I mean hey, if it's true, then I wanna know why, dammit.

Ahhhh, I just thought of a potential reason why. VM swap files. They can get fragmented, just like anything else, and if you don't have a nice tidy big chunk o' disk for them, it'll cause a slowdown. Since they're way over 20MB, they'll never be defragged. That's got to be it.

So... if you're running into several gigs of VM that is being actively swapped out a lot, and you are on a drive with little space, it is possible that your swap files will be fragmented, leading to some significant slowdowns.

Of course, a reboot will solve that...

My experience clearly differs from that, but then, I'm mainly on a 60 GB 5400 RPM laptop drive. Not exactly a performance wonder.

Ok, that 5-10GB is a pretty fixed amount in my experience, so it makes sense on a 40GB or 120GB drive. Obviously, the lower the drive size, the higher the %.

I suppose if you're really concerned about high performance, then keeping more open for the hot file system to do its mojo at the same time as the autodefrag, as well as smooth high datarate streaming... but still.

I'll reevaluate when I have my MBP.

'k.

Specifically, /System/Library/Caches, /Library/Caches, ~/Library/Caches, and if you're a heavy Safari user, ~/Library/Safari/Icons. Stuff like that.

Safari -> Empty Caches works well too.

Yeah, the OS is so stable that you sometimes forget that it's been running for so long. Rather unusual for a desktop OS.

Totally. Sometimes I have to stop and think "Now when the heck was the last time I even logged out??"

That just blows most people's minds... especially since I'm on a laptop that goes everywhere, bounces from network to network, and generally never skips a beat.

[chucker]

Originally Posted by Kickaha I'd love to see the reference, if you can find it. I mean hey, if it's true, then I wanna know why, dammit.

It was on AI (I think), around the time Panther came out. People were analyzing the code (since it's in Darwin) of Panther's on-the-fly <20 MB defragmentation; there was some kind of joke in there, and somewhere down the road in the thread someone cited an Apple engineer.

Ahhhh, I just thought of a potential reason why. VM swap files. They can get fragmented, just like anything else, and if you don't have a nice tidy big chunk o' disk for them, it'll cause a slowdown. Since they're way over 20MB, they'll never be defragged. That's got to be it.

I'll never quite understand the logic after which swapfile sizes are created. Starts with 64 MB, then 128 MB, then more. Old files never get purged (until reboot), or at least not for a long time. Seems like a very space-inefficient system, but on the other hand, it is most definitely a very performance-efficient system, at least compared to Windows and, yes, Linux. Sorry Linux advocates, but compared to OS X, your kernel's VM management sucks. It's really, really bad.

As for Windows: for some reason I fail to comprehend, its pagefile (which I assume is identical to OS X's swapfiles) does not get purged upon reboots. Instead, there's a defragment utility for that, PageDefrag, which I've found to be very helpful for performance. It can be run automatically upon each boot, and defragments parts of the registry as well while it's at it. Still, I'm confused as to why it wouldn't be easier to just delete pagefile.sys and have it recreated automatically.

So... if you're running into several gigs of VM that is being actively swapped out a lot, and you are on a drive with little space, it is possible that your swap files will be fragmented, leading to some significant slowdowns.

That may be it. Of course, that problem could be worked around if OS X were to purge "old" swap files (more quickly) as they become too defragmented, while running. Something for Leopard, maybe.

Of course, a reboot will solve that...

Sure, but reboots cost a lot of energy and downtime. I try and avoid them.

Ok, that 5-10GB is a pretty fixed amount in my experience, so it makes sense on a 40GB or 120GB drive. Obviously, the lower the drive size, the higher the %.

Common sense definitely suggests that it would be a fixed size, but my memory tells me that it was, quite clearly, 30%, regardless of actual capacity.

Safari -> Empty Caches works well too.

Except that it doesn't. I just tried, again, just to give you the benefit of the doubt, but ~/Library/Safari/Icons is just as large as it was before doing Safari -> Empty Caches….

That just blows most people's minds... especially since I'm on a laptop that goes everywhere, bounces from network to network, and generally never skips a beat.

Yeah, it was rather useful when I was a Windows admin. Wake up in the morning, open up laptop, have it configure itself for the home network through DHCP, do stuff, close lid, drive to work, open up again, have it configure itself for the network for the room I was in, etc. Walking around the building with my laptop was very, very convenient, and the availability of Remote Desktop Connection let me manage the Windows 2000 Server as if I had run Windows. The stability and reliability (as in: no "why does the network connection not work right now?") of OS X compared to that of Windows was downright mindblowing*.

*) I realized upon submitting that post that this was the very expression you used as well.

[Kickaha]

Originally Posted by chucker It was on AI (I think), around the time Panther came out. People were analyzing the code (since it's in Darwin) of Panther's on-the-fly <20 MB defragmentation; there was some kind of joke in there, and somewhere down the road in the thread someone cited an Apple engineer.

Well that narrows it down...

I'll never quite understand the logic after which swapfile sizes are created. Starts with 64 MB, then 128 MB, then more.

It's a classic allocation scheme - allocate a chunk of resources. When you run out, it's likely that you're going to continue to run out, so allocate *twice* that for the next level. Keep doing this. 64MB is enough to get the kernel and such up and running quickly even on a low-RAM machine. Another 128MB is enough to ensure a login is speedy. After that, 1/4GB chunks isn't unreasonable.

Old files never get purged (until reboot), or at least not for a long time.

Sort of.

Swap files aren't compacted, but they are purged, and generally within a couple minutes. Usually, if a user has needed X amt of RAM in the near past, they're going to need X amt again real soon now. So there's no point in doing a dealloc/realloc tango if you can just hang onto that space for a little bit, and see if it's going to be used again. Think about when an app crashes - the user almost always wants to get back up and running again ASAP.

The problem is, that the swapfiles are strictly FILO - so assume you launch, oh I dunno, Mathematica, and it gobbles up 3GB of VM. Then you launch TextEdit, which uses up maybe 100MB. You quit Mathematica. Unfortunately, the memory space used by TextEdit is up in swap file 12 or so, and active... so all those swap files are kept. Quit TextEdit, and then they start getting chopped away.

You're right, it's not perfect, and I really wish there was a compaction utility, but that's a really costly effort for regular use.

As for Windows: for some reason I fail to comprehend, its pagefile (which I assume is identical to OS X's swapfiles) does not get purged upon reboots. Instead, there's a defragment utility for that, PageDefrag, which I've found to be very helpful for performance. It can be run automatically upon each boot, and defragments parts of the registry as well while it's at it. Still, I'm confused as to why it wouldn't be easier to just delete pagefile.sys and have it recreated automatically.

NO idea.

That may be it. Of course, that problem could be worked around if OS X were to purge "old" swap files (more quickly) as they become too defragmented, while running. Something for Leopard, maybe.

Indeed.

Sure, but reboots cost a lot of energy and downtime. I try and avoid them.

I was just tying it into the rest of the advice. If he's going to be rebooting anyway, it'll take care of the swap files too, was all.

Common sense definitely suggests that it would be a fixed size, but my memory tells me that it was, quite clearly, 30%, regardless of actual capacity.

Hurm.

Except that it doesn't. I just tried, again, just to give you the benefit of the doubt, but ~/Library/Safari/Icons is just as large as it was before doing Safari -> Empty Caches….

*laugh* Okay, fine, fine... I thought it got the icons too. Mea culpa.

Yeah, it was rather useful when I was a Windows admin. Wake up in the morning, open up laptop, have it configure itself for the home network through DHCP, do stuff, close lid, drive to work, open up again, have it configure itself for the network for the room I was in, etc. Walking around the building with my laptop was very, very convenient, and the availability of Remote Desktop Connection let me manage the Windows 2000 Server as if I had run Windows. The stability and reliability (as in: no "why does the network connection not work right now?") of OS X compared to that of Windows was downright mindblowing*. *) I realized upon submitting that post that this was the very expression you used as well.

Great minds, yadda yadda yadda.

[chucker]

Originally Posted by Kickaha It's a classic allocation scheme - allocate a chunk of resources. When you run out, it's likely that you're going to continue to run out, so allocate *twice* that for the next level. Keep doing this. 64MB is enough to get the kernel and such up and running quickly even on a low-RAM machine. Another 128MB is enough to ensure a login is speedy. After that, 1/4GB chunks isn't unreasonable.

Sure, I get that. It just has a tendency to grow very fast, at least on this admittedly low-end machine (640 MB, 700 MHz G3). Within a day or two of use, I can be sure to have about 2 GB of swapfiles. The uptime right now isn't even 7 hours (due to an unfortunate event earlier today), and already, /var/vm takes up 512 MB. I don't mind, since I know it helps keep my system reasonably fast, but I do have to wonder whether this couldn't be optimized.

Swap files aren't compacted, but they are purged, and generally within a couple minutes.

Minutes? I assume by "purged", you mean that unneeded swapfiles get deleted altogether? If so, that's not my experience.

Usually, if a user has needed X amt of RAM in the near past, they're going to need X amt again real soon now. So there's no point in doing a dealloc/realloc tango if you can just hang onto that space for a little bit, and see if it's going to be used again. Think about when an app crashes - the user almost always wants to get back up and running again ASAP.

Affirmative.

You're right, it's not perfect, and I really wish there was a compaction utility, but that's a really costly effort for regular use.

If someone were to buy me, oh, I dunno, 2 GBs of RAM for my MBP, I won't have to worry about it as much.

I was just tying it into the rest of the advice. If he's going to be rebooting anyway, it'll take care of the swap files too, was all.

Sure.

*laugh* Okay, fine, fine... I thought it got the icons too. Mea culpa.

Sadly, it doesn't seem to, even though the Icons folder uses a caches-like directory structure. Must be a bug.

[Kickaha]

Originally Posted by chucker Sure, I get that. It just has a tendency to grow very fast, at least on this admittedly low-end machine (640 MB, 700 MHz G3). Within a day or two of use, I can be sure to have about 2 GB of swapfiles. The uptime right now isn't even 7 hours (due to an unfortunate event earlier today), and already, /var/vm takes up 512 MB. I don't mind, since I know it helps keep my system reasonably fast, but I do have to wonder whether this couldn't be optimized.

Only 2?? Jeez, I'll hit 7 or 8 no problem. But then, I'm doing research with large data sets, so...

Minutes? I assume by "purged", you mean that unneeded swapfiles get deleted altogether? If so, that's not my experience.

'Tis here. Get a large process going that consumes a lot of swap space. Watch swap files spawn like WV hillbillies on meth. Keep watching /var/vm after the process quits, and in a few minutes, they're gone.

Unless you trigger a process that gets put in the latest swap file, of course... which is very likely...

Sadly, it doesn't seem to, even though the Icons folder uses a caches-like directory structure. Must be a bug.

Yeah, we'll call it that.

[sirnick4]

Man guys.. get a ROOM

[chucker]

Originally Posted by sirnick4 Man guys.. get a ROOM

Yeah, don't mind us.

[faramirtook]

Yeah, only 2GB of swap strikes me as odd. I can run up to 5 pretty quickly, and I'm not dealing with all that leet hax0r stuff Kick does. I'm just running 12 apps with lots of tabs in Shiira. I also have about 50% (~25GB) free on my iMac. I only keep my system and apps on the internal disk, though. The external disk has backups and my home directory.

[Majost]

Man, the search engine at AI stinks. Google, however, is amazing

Aquatic is quoting it from (oh dear god) a Slashdot Comment.

[chucker]

Originally Posted by Majost Man, the search engine at AI stinks. Google, however, is amazing Aquatic is quoting it from (oh dear god) a Slashdot Comment.

Well, at least the number in my brain is correct. However, I recall a much more detailed post on this, and I recall the thread being a lot longer. Certainly more than just a single page. Maybe this was on MacNN?

[Enki]

<pokes head - ready to bitch-slap someone over defrag of HFS+>



</pokes head>

<updates database - there is intelligent life on this planet!>

[Dorian Gray]

Originally Posted by faramirtook Yeah, only 2GB of swap strikes me as odd. I can run up to 5 pretty quickly, and I'm not dealing with all that leet hax0r stuff Kick does.

Are you sure you're not confusing swap file size with the "VM size" stat in Activity Monitor? Kickaha and chucker are referring to the size of the swap files on the disk, not the VM size.

Regarding macsforever's question, I was blown away by Panther's on-the-fly defraging. It works incredibly well. Basically all files under 20 MB are guaranteed to have no more than eight extents. Large files are not defragmented on the fly, but who cares if a 500 MB file is scattered into even 100 parts? The difference in read speed between a 500 MB file with no fragmentation and one with 100 extents is unnoticeable without a stopwatch (and even then you'd have to be quick).

If you're curious, the demo version of iDefrag will give you fragmentation statistics for any drive, although it will only defragment drives smaller than 100 MB. (The iDefrag demo is non-invasive to install by the way.) I did a check on my iBook (1-year-old OS installation, pretty heavy daily use with the poor 30 GB hard disk often battered to within an inch of its life by video work - I often run to within a gigabyte of free space) with the following results:

- files with more than 10 extents: about 30, all of which are pretty big
- files with more than 50 extents: 12 (11 of which are more than 100 MB in size)
- files with more than 200 extents: 2 (both more than 300 MB in size)
- one file with 2282 extents (temporary 1.7 GB video file which was written to disk with about 700 MB free space left at the end)

So for me, defragmenting the disk would cause no noticeable speed increase but would waste a lot of time, entail a completely unnecessary risk of data loss, and cause a lot of extra wear on my 2.5-inch disk (not to mention heat) thus increasing the chance of disk failure in the future.

So would I defrag even if I had an app to do so sitting in my Applications folder? Hell no! It just wouldn't be worth it.

[Kickaha]

Originally Posted by Dorian Gray Are you sure you're not confusing swap file size with the "VM size" stat in Activity Monitor? Kickaha and chucker are referring to the size of the swap files on the disk, not the VM size.

Too true. I currently have 1.2G of swap files, and 8.44G of VM. The latter includes mapped files, where say a shared library is left where it is on disk as its own swap. (No sense copying the whole thing over to a swap file.) I've hit 6 or 7 GB of *swap files* before, meaning I was up in the 13-14GB of VM.

On a 512MB machine, with CPU pegged at 100% for several hours straight.

And able to still surf, check mail, IM... god I love a good solid VM system.

Regarding macsforever's question, I was blown away by Panther's on-the-fly defraging. It works incredibly well.

Ditto. After dealing with the defrag hell of NTFS professionally*, the difference is like night and day.

* A fresh reinstall of NT4, on a brand spanking newly formatted drive, would have 40-50% fragmentation after a *WEEK*. With the drive only 40% full. There is simply no reason for that other than laziness at MS.

[BarracksSi]

I recently defragged my iBook's 60 gig hard drive using a friend's copy of Drive Genius. While the process showed an improvement through its graphical representation, I still don't notice any performance difference.

I think it was a waste of time, really.

[Kickaha]

Not only that, but a number of drives now have the smarts to do a layout scheme for file access that looks fragmented from the outside, but actually takes advantage of things like rotational speed vs. cache coherence checks and other factors to provide an optimized constant data rate.

A defrag tool just screws that up, and can cause a degradation of access.

[Dave]

Originally Posted by Dorian Gray Regarding macsforever's question, I was blown away by Panther's on-the-fly defraging. It works incredibly well. Basically all files under 20 MB are guaranteed to have no more than eight extents. Large files are not defragmented on the fly, but who cares if a 500 MB file is scattered into even 100 parts? The difference in read speed between a 500 MB file with no fragmentation and one with 100 extents is unnoticeable without a stopwatch (and even then you'd have to be quick).

Speak for yourself. I've got a friend who's Nuendo rig sometimes doesn't even work if he hasn't done his defrag dance recently (before defrag = no worky, after defrag = everything running perfectly).

To answer your question, macsforever, I'd use the built-in defrag tools in Tech Tool Pro, but any decent disk utility package should have one. BTW, you do know Norton is spawned of Satan's own excrement, right? Don't use it. Ever.

[Kickaha]

Originally Posted by Dave Speak for yourself. I've got a friend who's Nuendo rig sometimes doesn't even work if he hasn't done his defrag dance recently (before defrag = no worky, after defrag = everything running perfectly).

He would be in the group of high-end professionals I mentioned earlier. He has a need for defragging. The average user? Nope.

BTW, you do know Norton is spawned of Satan's own excrement, right? Don't use it. Ever.

Ain't that the truth.