I encrypted my Time Machine backup (A Western Digital 2tb external drive) then realised that Airport wont mount the backup over wifi, so am currently decrypting the drive (via Disk Utility).

I found the command:

diskutil cs list

which shows me the progress of the operation (it took a while to register at the under the the menu-bar icon).

Here's a snippet from the output:

    Sequence:               13
    Encryption Status:      Unlocked
    Encryption Type:        None
    Encryption Context:     Present
    Conversion Status:      Converting
    Has Encrypted Extents:  Yes
    Conversion Direction:   backward

Encrypting the backup took about 24 hours, and the time machine icon currently shows 'Decryptig Backup Disk (28%)'.

My question is: can I eject the drive without losing the backup? Will the decryption continue when I mount the drive again?

TIA, Tim

2 Answers 2


I had to leave, so took a punt and ejected my drive. Timemachine took up where it left off when I remounted the drive, no problems!

  • I should add a warning to this answer: I had additional backups, and your mileage may vary - exercise extreme caution! At a guess, this answer was probably relevant to OSX10.7 - no telling what might change with time!
    – ptim
    Commented Mar 7, 2014 at 5:54

I would say no - I ejected a decrypting drive (it was decrypting due to me not ticking "encrypt" when adding it back to the computer and it then starting to decrypt) and on reconnection it a/ does not appear and b/ in Time Machines Preferences reports 0 bytes.

In disk utility the drive is detected, the logical volume is greyed out and will not mount.

  • It does sound risky, hence my original question! Curious to know: if you run diskutil cs list - is there any output? maybe the disk is still decrypting for you?
    – ptim
    Commented Mar 7, 2014 at 5:56

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