I have a MacBook with a Momentus XT hybrid SSD+HDD drive. It have a 500GB HDD plus 4GB SSD which, as I could check, it uses as a cache for read operations. It uses some kind of black magic to determine the most used data and let it easily accessible through the SSD storage.

I wonder if I can enable FileVault 2 to encrypt this drive and if it will kill these feature of the hybrid drive.

I know that FileVault always lead to a performance penalty, but my wonder is if the drive will become unable to determine the portion of data that can be SSD-boosted due to the fact that it will become encrypted.

  • Encryption and SSDs don't mix well, mainly due to the way wear-levelling works. However, I doubt the SSD portion will even be used by FileVault.
    – user479
    Sep 2, 2012 at 3:29
  • @RandolphWest It would be great if you answered the question explaining how wear leveling does or does not affect OS X in practice.
    – bmike
    Jun 20, 2013 at 17:09
  • I have no experience of wear-levelling with OS X, only Windows. The TrueCrypt documentation (truecrypt.org/docs/wear-leveling) says that if you're doing in-place encryption, wear-levelling affects how the data is physically stored on disk, so multiple versions of the sectors may appear, which contain the unencrypted data. A container like FileVault will not suffer from this with newly-created data because it won't ever stored decrypted data. It's the existing data that is the issue.
    – user479
    Jun 20, 2013 at 22:25

1 Answer 1


FileVault 2 encrypts the filesystem at a block level. Despite the data being encrypted the cache in your disk should still be able to work out that particular blocks are being accessed more often and cache them in the SSD.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .