Erasing a FileVault 2-encrypted Volume
On occasion, it’s necessary to erase a FileVault 2-encrypted volume. However, Disk Utility won’t let you erase or repartition until you unlock or decrypt.
This can be an issue for a malfunctioning FileVault 2-encrypted volume that will not let you either unlock or decrypt. To help with this, the diskutil tool provides a way to quickly delete CoreStorage volumes. This includes the ability to erase encrypted CoreStorage volumes (aka FileVault 2-encrypted volumes) without first decrypting or unlocking them.
To do this, first run the following command:
diskutil cs list
This will give you with a list of the CoreStorage volumes on your system. Unless you have a Fusion drive or multiple encrypted drives, your FileVault 2-encrypted drive should be the only one listed.
In the listing, you will want to select and copy the Logical Volume Group (LVG) alphanumeric UUID for your CoreStorage volume. The LVG should be the first UUID listed and it’s the one we want to delete.
Next, run the following command:
diskutil cs delete UUID_here
This will delete your CoreStorage volume and reformat it as an unencrypted HFS+ volume.