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Is there a native/third-party utility (or native trick) to move large, frequently-used files closer to the center of the disk?

I was under the impression that the OS tried to automatically optimize frequently used files to be closer on the center of the disk, but I don't know how "frequent" is "frequent enough" and would like to force an entire project directory to be moved closer on disk.

The reason: I'm using Logic Pro for several projects, but on one particular project, I keep tapping out the Disk Activity (as evidenced by "System Overload" messages from Logic and spikes in the Disk Activity view of Activity Monitor).

I've seen some users of Logic and Final Cut have performance improvements after a defrag (using iDefrag), but was wondering if there were any other options other than a forced defrag.

Suggestion: Could copying the entire project directory to an external drive, rewriting it to the local disk as a single I/O operation, and then waiting for the file system to index/optimize it help? Or would that reset the access "frequency" and actually hurt?

Specs of machine in question:

  • OS X 10.7.4
  • 500GB Serial ATA Drive @ 7200
  • 2.66 GHz i7 MacBook Pro
  • 8 GB 1067 MHz DDR3
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This is exactly what SSDs and RAID arrays are for lol – XAleXOwnZX Sep 8 '12 at 18:17
I couldn't agree more. Too bad I have neither on this setup... But I will before starting the next album! – Old McStopher Sep 9 '12 at 17:23

1 Answer

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There’s not much difference between moving the files to the centre of the HD or towards the periphery. The centre you see in visual representations is just that, a rectangular visual representation of your circular. Physically, the file may be anywhere on the disk.

Deleting and rewriting the file won’t help much, as the space on your disk is already fragmented. Though I have not confirmed it, OS X defragments files below 20 MB automatically. Audio and Video files tend to be large than 20 MB, and are highly fragmented.

Assuming you are talking about defragmenting the disk, I highly recommend iDefrag. I use it every 6 months, and using the computer after the defrag is like switching from an old 56k modem to Google’s fibre optics.

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Good info, but know that there is a tangible physical difference between locations. Arc Length = 2pi(r)(CentralAngle/360). Longer distance traveled requires more time. – Old McStopher Sep 6 '12 at 17:26
That’s like 4ms. Disks are pretty fast. – duci9y Sep 6 '12 at 18:13
Time to traverse a block is a function of the CentralAngle, not of arc length. Or put another way, the surface speed and arc length both increase proportionally to radial location of the track; their ratio stays constant. Where there can be an improvement in speed due to file position is from the heads having to move less distance radially to reach the desired track, but this is only realizable if you know where the heads tend to "hang out" and you can position the files in question nearby. ... – JRobert Sep 6 '12 at 18:56
... The other variable is the rotational latency but this is almost always random, i.e, unpredictable. (Historical trivia: On some of the (now ancient) old drum-memory computers, some programs were carefully optimized to place instructions on the drum where the heads were predicted to be when the previous instruction finished.) – JRobert Sep 6 '12 at 18:59
Good info, but you can just defragment a file, which will not require the heads to move from one place to another. That way, the heads will travel to the starting block, read the data in one go (probably broken into a few pieces) and go back to something else. – duci9y Sep 7 '12 at 8:55
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