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I chose a 1T external drive for time machine and checked the "encrypt backups" option. I thought it will only encrypt the backups, but as it seems it is now encrypting the whole drive which has quite some data on it and is not SSD ;). Is there a way to cancel the encryption process? I turned off Time Machine and chose another drive for it.

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Whatever you do, let the process finish, backup everything, then tinker with the settings. If you mess up while your files are encrypted, you are royally screwed. – Thomas Aug 15 '12 at 0:22
This is my only real complaint with OSX. Once the process is started some machines basically become unusable. It shouldn't be this easy to render my workstation unusable for the next 3 days: This is OSX and it's not Linux, they are supposed to be protecting me from myself. Until now I've never thought twice about clicking a dialog in OSX. Thanks Apple. – Nathan C. Tresch Sep 30 '12 at 23:56
up vote 19 down vote accepted

Yes, in 10.9+ you can roll it back while its busy encrypting

diskutil cs revert /Volumes/title_drive -passphrase

You will then be promted with the OS X password unlock/decrypt dialog. After that it starts decrypting. The title_drive you can look up with diskutil list or ls -al /Volumes

Check the status with

diskutil cs list

Look for "Conversion Progress" and check if "Conversion Direction:" is set to "backward"

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Thank you, this worked a treat. Otherwise i would have had to wait ~6 days for it to encrypt my filesystem! – Tom Beech Jan 6 '15 at 20:46
What if I forgot my passphrase? :-/ Guess I will have to unplug the drive and wipe the GPT on a Linux box... :) – Lester Cheung May 19 '15 at 12:24
If you have a bootable usb key you could run disk utility and delete the disk partition there and repartition it. But of course you lose all data. I don't know if the rescue partition is accessible without unlocking the drive, I thought FF2 was full disk encryption instead of only individual partitions. – Sanne May 19 '15 at 16:00
Thanks - went with the Linux route because it's an external drive. Cheers! – Lester Cheung May 20 '15 at 11:32
@William Too late for you, I know, but I had the same problem and managed a fix: open Disk Utility; first aid the partition; open a new System Preferences window; navigate to FileVault; disconnect and reconnect power cable. The panel should now say 'Decrypting...' – J.B. Jul 1 at 23:20

Maybe try highlighting the drive in disk utility, go to "File > Turn Off Encryption". If that isn't possible while the encryption is in progress, there probably is no 'nice' way of stopping it. In that case your best bet would be to wait it out, or risk making a mess - Like Thomas said.

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Encrypting of the FileVault -- You can't stop it, if you try it'll mess up your whole MacBook Pro. No fun. Just let it do it's thing, takes 3-4 days, usually.

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Like I said before, under the system utilities, go to "disk utility" then find which harddrive is being encrypted by going under file and look for "Turn off Encryption", toward the bottom of file; when you find the one you need and click on it, it takes maybe 10 minuites... encryption takes a LONG time.

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This is not an answer to the original question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. – DavidPostill Nov 11 '14 at 21:33
I don't have the option for "Turn off Encryption" in Disk Utility in El Capitan – William May 18 at 17:45

Then reset pram with option+cmd+p+r
Booting with cmd+r the utility disc (I have a macintosh HD and one partition encrypted (the one with encoding paused)) >select the partition encrypted>click file and unlock>repair the partition disk>repair permission on partition>repair macintosh HD
The encryption will be resumed

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