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Mac OS X 10.3 Defrags Automatically

Posted by pudge on from the hot-character-adaptive-respawning dept.

EverLurking writes "There is a very interesting discussion over at Ars' Mac Forum about how Mac OS X 10.3 has implemented an on-the-fly defragmentation scheme for files on the hard drive. Apparently it uses a method known as 'Hot-File-Adaptive-Clustering' to consolidate fragmented files that are under 20 MB in size as they are accessed. Source code from the Davwin 7.0 Kernel is cited as proof that this is happening."

5 of 181 comments (clear)

  1. Re:Necessarily Useless by Dan+Ost · · Score: 2, Insightful

    Umm, isn't the HD the bottleneck of modern systems?

    Isn't the reason all these high performance machines have so much RAM so that
    they don't have to take the enormous hit of swapping to disk?

    Even ram is too slow. That's why they're putting so much cache on the chips now.

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    *sigh* back to work...
  2. think outside the /. by BortQ · · Score: 4, Insightful
    It seems as if the /. crowd isn't all that impressed by this advance by apple.

    Well that's fine. The real upside of this is for people that have never heard of /. and don't really know what a hard drive is, let alone know how to defrag one.

    Previously these people would just go forever without defragging. Now they can still do that, because Apple is doing it for them behind the scenes.

    This is yet one more example of Apple's winning philosophy: Keep it simple, make it better.

    --

    A Multiplayer Strategy Game for Mac OS X, Windows, and Linux
  3. Re:Amortized cost... by bdsesq · · Score: 5, Insightful

    Noting this, the fastest way to get data off a drive might not be a straight line.

    This is true. However it is also true that a defrag does not have to put the data in physically contigious blocks. It can just as easily put the data in whatever configuration makes retrevial work fastest on that particular drive geometry.

    This means that an intelligent defrag can improve performance.

  4. information by djupedal · · Score: 3, Insightful

    Try this...

    ...and this...

  5. Re:I think it's... by coolgeek · · Score: 2, Insightful
    Perhaps reading the source will reveal some insight for you all as it has for me. The defrag takes place on an hfs_open call, thus the disk, if not spinning at the time, will be powered on shortly. It also is NOT a background operation, and only applies to files that are being opened.

    I believe the rationale is that it takes little more than the same number of IOs to defrag as it is going to take to read the file once, and will take less IOs on subsequent accesses to the file (after defrag), which would appear to be imminent because the file has just been opened.

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    cat /dev/null >sig