compress/defragment NTFS VM?

Discussion in 'Parallels Desktop for Mac' started by patches, Nov 1, 2006.

  1. patches


    Sorry if this has been answered elsewhere, I couldn't find it...

    Is there the same benefit from compressing and defragmenting NTFS volumes in Parallels VM HDD's as there would be with physical disks?
  2. patches


  3. unused_user_name


    Defragging, yes.

    Compressing? As in running the compressor in Parallels? There is no real hardware equilivant to running the compressor in Parallels.

    As for NTFS compression, that is generally a bad idea in both real hardware and in Parallels.
  4. joem


    Yes, you get about the same benefits (and costs) from both defragging, and using NTFS compression.

    Unfortunately, life isn't quite that simple though. If you defrag the virtual disk, you will have fewer VIRTUAL seeks to read a file, but if your Mac HD is fragmented, and the file you are reading is in several OSX fragments, OSX will have to seek to get them all. This means that if your virtual HD FILE in OSX isn't fragmented, the benefits of de-fragmenting the virtual disk will be similar to what you would get on raw hardware, a fragmented OSX file will reduce the benefits the same way a fragmented hardware drive would on a real PC. The fact that OSX caches real disk activity also complicates the picture.

    As to NTFS compression, it's a time / space tradeoff. It's a great idea for large infrequently accessed files if you want to save the space. For frequently accessed files larger than 4k (approximately, and assuming NTFS defaults) you will suffer a performance hit from the CPU cycles required to handle compression, but gain from the reduced I/O required. This tradeoff may reduce performance, or actually improve it depending on the application's CPU requirements and the speed of your disk channel. Note too, that some files such as text benefit more from compression than others. ZIP files, for example, are often slightly larger after NTFS compression.

    Blanket statements about the desirability of any options are generalizations, and as the joke goes, all generalizations are wrong.

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