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Time Machine + FileVault on Lion or Mountain

During a Time Machine backup, is the backed up data at any time unencrypted?

  • If yes: can I disable that at the cost, perhaps, of time/space?
  • If no: why does the system say "Encryping..." when I stop a running backup before returning the Time Machine state to "waiting for next backup"?
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The command diskutil cs list | egrep -i "size|status" will show how much of the drive is currently encrypted as well as the conversion status. – bmike♦ Oct 2 '12 at 23:52

marked as duplicate by patrix♦, Gerry, gentmatt, Stu Wilson, daviesgeek Oct 4 '12 at 19:13

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2 Answers

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The new FileVault is a whole drive encryption, so Time Machine doesn't do any sort of encryption. The kernel / OS handles encryption as the data gets written to the drive so it's an all-or-none type of thing.

Once encryption is on for a specific drive, all new writes are encrypted whether or not Time Machine or another process is writing. The "Encrypting..." status is transient where the system is going through every block on the device and encrypting it so short of disabling the entire drive's setting to be under FileVault control there is no way to opt out of encryption for some new writes while leaving the encryption enabled.

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"the system is going through every block on the device and encrypting it": so, in which state was the data before this encryption if it needs to be encrypted? I am confused... – Robottinosino Oct 2 '12 at 18:55
So - for the encryption to work, each block needs to be written. Even if there is a zero or no data, the encryption reads what was on each sector and then passes it through the encryption so that when it is read later, it comes out correctly. Basically, there is some value on every block of storage whether the OS has allocated a file there or not. This happens normally during the initial window before the entire drive is processed and has passed into the "everything is encrypted" state. – bmike♦ Oct 2 '12 at 19:09
This "Encrypting..." message appears even after the initial encryption? I will add a picture to prove that. – Robottinosino Oct 2 '12 at 23:30
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You have a problem if that message is continuous. You can use the command diskutil cs list to determine if your conversion has completed and also watch the Disk Activity from Activity Monitor to ensure things are moving along if your core storage Logical Volume Family is still converting. – bmike♦ Oct 2 '12 at 23:38
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According to this page, there is an "Encrypt backup disk" available when you add a new Time Machine disk in Lion.

Starting in Mountain Lion, OS X gains the ability to encrypt (and decrypt?) existing Time Machine drives.

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Any core storage volume can be encrypted - this isn't about Time Machine other than it's the way most people enable encryption since they don't go to Finder or Disk Utility or the command line to set up file vault. – bmike♦ Oct 2 '12 at 19:11

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