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I was using (Legacy) FileVault on Snow Leopard and when I upgraded to Lion, it kept me on Legacy FileVault. I notice that FileVault uses a lot of disk space which is then recovered once I log out. Sometimes this can be in the range of 5-8 GB. I'm thinking about switching to the new FileVault in Lion, but I'm wondering how the disk usage is compared to Legacy FileVault.

Does the new FileVault in Lion use up more or less space than Legacy FileVault? Will it continue to use up a lot of space temporarily (i.e. after a restart it will free up all that space)?

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The two technologies share nothing except the name and cannot be directly compared. The old Filevault created a spare bundle image file for your home folder, which was encrypted. The new one simply encrypts the whole drive in a way that is invisible to the user.

If anything there may be a slight overheard to managing a sparsebundle which will not be there for whole disk encryption, but I doubt that it will be significant enough to make it a part of your decision to use it or not.

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    Unless I misunderstood your answer, I disagree. The sparse bundle storage format had all the downsides of a filesystem where file changes and deletions are not performed until an offline compact operation is triggered. For an empty folder, the original overhead is perhaps 400 MB less, but in practice the new system has no incremental or variable overhead and is far superior in practice from a storage efficiency standpoint.
    – bmike ♦
    Mar 19, 2012 at 20:41
  • I suppose it depends on your definition of 'overhead', certainly as @kylecronin described there are issues which I perhaps glossed over here (but won't repeat as his says it all), so take this answer in context with Kyles.
    – stuffe
    Mar 19, 2012 at 20:46
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    Between the three of us - hopefully no aspect of this remains unanswered :-)
    – bmike ♦
    Mar 19, 2012 at 20:51
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As Stuffe said, the two versions of FileVault are based on completely different technologies. The implications for disk space, however, are not trivial. The new FileVault is block level full-disk encryption, and as such exists completely outside the filesystem, and therefore it takes up zero filesystem space. It might take up a small amount of actual disk space, but the number you see when you "Get Info" your disk in Mac OS X will never be affected by Lion's new FileVault.

The old FileVault, however, was implemented within the filesystem - like Stuffe said, it was an encrypted sparsebundle for every user. This had implications such that if lots of space were allocated to the sparsebundle while it was mounted (while the user was logged in) it could only be reclaimed when it was unmounted (when the user logged out). I'd been in that situation many times myself, knowing that running of of space on my drive meant I had not only to trash some files but go through the agonizing process of logging out and waiting who knows how long to let Mac OS X reclaim some of that space. The new FileVault in Lion removes all of that.

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Yes - the overhead required by the new file vault encryption takes less space than the old FileVault implementation. Often ten or more gigabytes less space on drives in the 250 to 500 GB size and normal moderate file usage of photos, music and light video storage needs.

The new implementation uses only a fixed amount of space to handle the storing of the keys needed to decrypt the core storage. Most drives reserve 650.0 MB of space for the recovery HD that is created (or used) when you encrypt a whole disk in Lion using File Vault.

The older implementation stored the user folder only in a sparse disk image which resulted in slightly less initial overhead to create the key storage space and the initial directory to track the files within the sparse disk image. However, in use, files are marked for deletion and not actually deleted until a later "reclaim" or "compact" the storage and reclaim space that was used by this method of encrypting the files. It was not uncommon to have tens of gigabytes of space in normal situations where users had File Vault enabled on pre-Lion OS.

When you switch to the new encryption - you no longer need any compact time or delay. The overhead is fixed and constant. This alone is a great benefit even before you take in account how the new logical volume stops breaking apps since the encryption is totally transparent to all applications.

As usual, John Siracusa's review has a great dissection of the changes that Lion made to FileVault.

In addition the new implementation can be enabled and disabled on the fly and the machine will handle encryption/decryption without needing double the space of the files to hold the intermediate files during decryption. With the old FileVault you could literally be stuck and unable to turn off decryption if the free space was smaller than the folder payload size. You couldn't decrypt in place and instead needed to copy the data out piecemeal or get a spare drive to hold the decrypted contents when you turned FileVault off.

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  • I think the space overhead is to an extent trivial on a modern reasonable sized drive, having said that the "management overhead" of farting around effectively requiring maintenance every time you log out is perhaps not to be ignored.
    – stuffe
    Mar 19, 2012 at 20:47
  • I would agree that in both cases - less than a GB of overhead is trivial, but in practice a user with 50 GB of files will see noticeable improvement on how much free space is left if they choose one over the other. Even after a compaction, things like file compression are not active on the older FileVault resulting in more disk space to contain files before Core Storage. The farting is far worse a sin in my mind (and the dreaded - you don't have enough free space to compact or turn off FV even worse.)
    – bmike ♦
    Mar 19, 2012 at 20:51

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