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Back up and erase
Authored by: johnsawyercjs on Dec 14, '04 01:33:28AM

I don't know of any on-the-fly, background defragmenting utility for OS X, except OS X itself (see messages above for how this works). Alsoft has a fine background defrag util for pre-OS X, called DiskExpress Pro, but there's no OS X version--in fact, there's no HFS Plus version, even though HFS Plus was introduced with OS 8.1. For several years, Alsoft has had a running "gag" on their web site, in which they've been promising "The version that will optimize HFS Plus disks is currently under development". When OS X was released, they started promising an OS X version. Several years ago, I stopped by their booth at the San Francisco Macworld show, and asked them if they were ever really going to release an HFS Plus version. The two guys in the booth first laughed as if they'd been caught in the act, pointed at each other to try to get the other guy to answer the question, and then one of them responded that it would be available in about a half-year. That was several years ago. I'd say it's safe to say they have no plans to release this, so when you still read on their web site that it's "currently under development", well, they have an odd sense of humor.

The fastest and safest way to defrag a hard drive is to back it up to another drive (for OS X boot volumes, use any of the utilities that can create and restore a bootable backup), erase the source drive, then copy the files back to it. You'll wind up with the useful byproduct of a backup in the process. The Finder, and most backup utils, will copy files back to the erased drive in a contiguous (non-fragmented) fashion. After this, any files that you add, or existing files whose size you increase, won't stay defragged (except when OS X does it), but the rest will stay put and defragged. Defrag utils run the risk of moving just one block to the wrong location, or a power outage or a crash, and you can lose some files or even everything. This is very unlikely, but I've seen it happen--several of my clients brought drives to me years ago, where this had happened when they used various defrag utils, including early versions of DiskExpress and Norton's SpeedDisk.

However, there aren't many instances where defragging a drive, or keeping your drive defragmented, is useful:
• Some applications that frequently or constantly access one or more data files, like a graphics or movie file, may run faster when these files are defragged. If you can use a util that will defrag only specific files you select, that's best.
• When so many files on the hard drive are fragmented, that the hard drive directory's extents file is used up (it keeps track of where the blocks of fragmented files are located)--there are only a certain number of blocks allocated to the extents file, and when these blocks are all used up, new files and new blocks in existing files, begin re-using these extents blocks, resulting in "overlapping" files. This was more of a problem under pre-X--it's unlikely to happen under OS X.
• OS X's virtual memory swapfiles need to be contiguous, so if there isn't enough contiguous free space on the drive where the VM swapfiles are stored (the default is the startup volume, unless you've messed with the prefs using a utility that lets you), there may be extra disk thrashing while OS X moves blocks around until it creates enough contiguous free space for the VM files. However, as I understand it, OS X handles this task fairly well, so that once it clears up some space, that space is available for a while for swapfiles, until it has to be done again (somebody enlighten me if I'm wrong).
• Some print spool operations may be faster, but this may be limited to specific types and/or sizes of documents.



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Back up and erase
Authored by: bdjones on Dec 16, '04 11:18:42AM

Intech Software Speed Tools has a disk defragmenter as part of it's suite. Works with 10.3.x



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Back up and erase
Authored by: johnsawyercjs on Dec 20, '04 12:41:27AM

Yes, but doesn't it require that you launch the Intech utility to start the defrag process? I don't think it operates on the fly, in the background. If it allows you to do other things while it's running, that would be close to the same, but not quite.



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Back up and erase
Authored by: ericdano on Dec 28, '04 12:07:50AM

No, it doesn't run on the Fly, but it does a good job defragmenting drives. I use it a lot to defragment my Audio drive for recording. It's a great little tool.



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