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I am selling my MacBook Pro and was reading through what to do before factory resetting the Mac. One of the recommended steps was turning off FileVault, but now I want to reset the hard drive and reinstall the OS and I'm stuck waiting for FileVault to do it's thing. I'm not sure how long FileVault will take but I don't want to keep the purchaser waiting and he's coming by in about 18 hours.

Can I erase the drive halfway through the FileVault decryption process without it causing problems for the Mac? I'd imagine that if I'm erasing the drive the FileVault status won't matter too much but I'd like to be certain.

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    Who recommended you turn off FileVault? – tonychow0929 Jul 14 '18 at 12:33
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    Turning off Encryption is pretty much the stupidest thing someone could suggest to you. I would not trust anything this source says. If you hadn't turned off Encryption, all you'd need to do is not tell the buyer the password, and there would be no way in hell that they could ever access your data. Now that you have decrypted (half) your data, you need to perform additional steps to ensure they can't access it. – Jörg W Mittag Jul 14 '18 at 12:38
  • Just to further clarify how FileVault works, if the whole disk is encrypted, it’s encrypted. All that needs to be done to safely wipe the disk is reformat it. This is like an iPhone or an iPad where a factory reset takes seconds because—by default—iOS does it’s own equivalent of FileVault. When you reset an iOS device it just tosses the keys and declares the system space as “free.” There ain’t no way that space will come back in readable form. – JakeGould Jul 15 '18 at 0:36
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The secure way to do it is to simply erase the dive, don't decrypt it first. That makes recovery of your data impossible - whereas if you decrypt it, there is a possibility it can be read later by a bad actor.

See Apple KB - What to do before you sell or give away your Mac

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You can wipe it without decrypting. Just use disk utility first when you are in the installer system and format the drive you are installing to.

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