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I set up Time Machine in Mountain Lion by plugging in a newly formatted 500GB USB drive, selecting that from the Time Machine dialog, and checking the box to encrypt my backups. A window appeared that said "Preparing disk [diskname] for encryption." The progress bar quickly filled to about 80% and then stalled there. It's been about 22 hours now with no sign of progress. I know encrypting a drive can take a while, but is this too long? Should I force quit or unplug the drive and start over?

Notes:

  • I checked the system log to verify that the computer's been up and working all night; it didn't go to sleep.
  • The drive is no longer showing up in the finder or Disk Utility. Is that normal when encryption is in progress?
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    This is certainly very long. I encrypted a 300 GB Time Machine Drive in about 6h yesterday. (connected via USB 3.0)
    – gentmatt
    Dec 7, 2012 at 19:52

2 Answers 2

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22 hours is very long indeed. I have encrypted a 1TB drive in less time before.

The encryption is handled by a "live background process". "This process continues seamlessly across reboots. The logical volume remains usable at all times."

from man page > diskutil > encryptVolume

Maybe this daemon hangs or simply halted because the drive is not mounted (which is fine). So you should just re-mount it again.

Alternatively, I would try I restart the daemon by simply restarting the computer. Once the Time Machine backup is mounted again, the daemon will continue encrypting the drive.

Checking the encryption progress using diskutil

You can check the status of the encryption by using the command:

diskutil cs list

In the nested tree you will see a Logical Volume Family which is currently being encrypted. If you drive is being encrypted, you should see the entry Conversion Status: Converting .

Encryption Status:           Unlocked
    Encryption Type:         AES-XTS
    Conversion Status:       Converting      //what does it say here?
    Conversion Direction:    forward
    Has Encrypted Extents:   Yes
    Fully Secure:            No
    Passphrase Required:     Yes
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    This is an incredibly useful answer, thank you. I decided to abort the process shortly before reading this, so I can't test it myself. The drive has been having serious problems since then, even after reformatting, so I suspect something is going wrong with it.
    – octern
    Dec 7, 2012 at 23:54
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    Being used to the above, I was quite surprised that erasing a disk and enabling encryption in Disk Utility, and then copying lots of data to that empty disk, shows "Complete" right after the copying is done. But erasing/encrypting a disk and then use that for Time Machine indeed needs a looooong encryption process after the first backup is complete. (So, both start with an erased and encrypted disk. Actually: I'm more surprised that Time Machine uses a post-encryption step if the disk was already marked encrypted when erasing it.)
    – Arjan
    Mar 14, 2013 at 9:24
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    Also you can see progress of conversion with this entry: Conversion Progress: 11%
    – ersentekin
    Nov 19, 2015 at 15:50
  • In Mojave (probably earlier too), the Time Machine icon in the menu bar will give you "Encrypting Backup Disk... (29%)" and that number may never change, but the progress percentage from diskutil does actually go up! (Looks like the progress bar in Time Machine preferences is also correct.) Thanks for giving me a reason to wait for completion!
    – idbrii
    Jan 20, 2019 at 21:10
  • @Arjan Did you ever manage to figure this out?
    – sunknudsen
    Apr 2, 2021 at 11:42
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The backup process was hanging on Encrypting task for me on Catalina 10.15.5 when formatted my pen drive using Mac OS Extended (Journaled) system. I cancelled the job, reformatted using Disk Utility and Mac OS Extended (Journaled, Encrypted) forrmat and a couple of minutes it’s started backing up (54GB estimated 2 hours).

The above is way quicker than letting the Time Machine to reformat the destination drive, backup data and then encrypt. I also disabled Time Machine Automatic backups for the first backup just in case so it doens’t try to backup while the first one is still progress.

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