iMac Fusion Drive perfomance loss with File Vault

Discussion in 'iMac' started by Schwertleite, Aug 19, 2015.

  1. Schwertleite macrumors newbie

    Aug 19, 2015

    I got the Retina iMac with a 3TB fusion drive. When I originally used Blackmagic’s speed test I measured a disk speed of around >300 Mb/s write and >600 Mb/s read.

    Now I have turned on file vault and I seem to constantly measure a reduced speed of up to 200 Mb/s write and up to 500 Mb/s read, which is effectively a 20%-30% perfomance loss. This is much higher than the usually marginal perfomance loss associated with disk encryption.

    Is this to be expected? i.e. that the Fusion Drive algorithms cannot fully cope with File Vault?

    Any thoughts are much appreciated.


  2. Weaselboy Moderator


    Staff Member

    Jan 23, 2005
    BlackMagic uses incompressible data for its tests, and FV2 is known to be a little slower with incompressible data. Try another test like Aja and see what you get. But there will be some slight write slowdown with FV.
  3. BobertKennedy macrumors member


    May 3, 2014

    Slower read/write speeds are the result of file vault encryption/decryption, although there are other factors at play such as the processing power of your CPU. This is normal. See for more details.

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