How to erase hard drive where nothing is recoverable

Is that even possible?

Absolutely.

To correctly sell or transfer ownership of a Mac, even to someone in your family, you should follow these instructions.

Refer to What to do before selling or giving away your Mac

1. If you enabled FileVault, disable it in System Preferences > Security & Privacy.
2. "Deauthorize" your iTunes account. Same for Audible if you have one.
3. System Preferences > iCloud > de-select "Back to My Mac" and "Find my Mac".
4. Sign out of iCloud. Select "Delete from Mac" when it appears.

Next: Remove all your personal information by completely erasing the Mac's internal storage.

1. If your Mac shipped with a grey System Install DVD, start your Mac with that disc inserted in the optical drive while holding the c key to boot from it instead of its internal volume, which should be erased before selling it.

   Apple stopped shipping Macs requiring those discs in August, 2011.

2. If your Mac did not ship with discs, boot OS X Internet Recovery:
   • using three fingers press and hold the following keys: ⌘(command), option, and R.
   • With a fourth finger press the power button to turn on the Mac.
   • Keep the other three fingers where they are until you see the "spinning globe" icon.
   • This method forces the Mac to download its originally installed OS from Apple's servers, which will not require an Apple ID to install.
3. Remove any Open Firmware password if you created one: select Firmware Password Utility from the Utilities menu and remove it.
4. Select Disk Utility from the Utilities menu.
5. Remove any partitions you may have created.
6. Select the Mac's hard disk icon, then select the "Erase" tab.
7. Select the "Security Options" button and erase the disk.
   • The more "securely" you erase the disk, the longer it will take.
   • The fastest method is sufficient since all but the most expensive techniques and equipment will be able to recover securely erased data.
8. When it finishes, quit Disk Utility.
9. Select Install Mac OS X from the Utilities menu.
   • An Apple ID will not be required. If a prompt for an Apple ID appears, return to Step 5.
   • Do not create any user accounts.
10. When it finishes, shut down the computer.
11. If you want to install the bundled apps that were included with your Mac, restart by using your Applications DVD if one was included, and install the bundled apps.

    Apps bundled with newer Macs that shipped without discs cannot be transferred. Its new owner must purchase them from the Mac App Store using his or her own Apple ID.

If the Mac is being sold to someone outside the family consider the following additional information:

1. System Install DVDs that came with your Mac should remain with it forever, and must be included with the sale.
2. Consider including your AppleCare certificate if you bought it, printed documentation, even the box if you still have it.

   AppleCare stays with the equipment and is transferable.

3. Execute a bill of sale showing the Mac's serial number.
4. Once no longer in your possession, remove the Mac from your devices in My Support Profile.

So essentially, since I cannot keep encryption on because it would render the hard drive useless for the buyer, there's not a way to make my information unrecoverable?

No. You leave the drive encrypted, but use Disk Utility in Internet Recovery to erase the entire SSD--choose the device itself, not Macintosh HD. Once you do that the encryption key will be destroyed and there is no way to Decrypt the data that remains. The drive will function normally as an unencrypted drive.

One also said that as long as I have FireVault encryption on and I format, there is no way they could get in information since it is encrypted with a password.

That is 100% correct, but if you were to leave the disk encrypted your buyer would not be able to use the Mac at all. To ensure a pleasant transaction you need to follow the instructions I posted.

Since you encrypted that disk with FileVault, using any multi-pass erasure option is unnecessary.

Since you encrypted that disk with FileVault, using any multi-pass erasure option is unnecessary.

But, according to the steps posted above, you decrypt the drive and disable FileVault before erasing the disk. So, the disk is no longer encrypted.

Is it not possible to format the drive in IR while encrypted? That should remove the "encryption," but leave the data in an irrecoverable state. I have done that successfully on a flash drive, but not yet on a HDD or SSD.

Using a multi-pass "secure erase" is unnecessary, and inapplicable to the flash memory used in a Retina MBP. It will accomplish exactly nothing, other than contribute to its finite read/erase cycle limit.

As Barney-15E graciously pointed out, erasing your Mac's storage with Disk Utility while it's still encrypted will leave its contents encrypted and inaccessible. Other than removal and destruction of the component itself, encryption is the only way to secure flash memory, due to the way it works.

For what it's worth the multi-pass "secure erase" option could not guarantee reliable data destruction even with traditional hard disk drives either. That's the reason Apple got rid of it in later macOS versions.

To be clear a Retina MacBook Pro does not have a hard disk drive. It uses flash memory, which may or may not be a replaceable module you could obtain from Apple or an aftermarket source. Either option would not be inexpensive or convenient, nor should it be necessary. Erasing it first with Disk Utility, and then removing the FileVault password will accomplish exactly what you want to do.

I only had a Flash drive to play with, so I'm not sure if that will affect the results.

I was able to Erase the encrypted hard drive.

However, I don't understand why you get the old Disk Utility if you are running Sierra.

For the old versions that you are seeing, were you able to select 1-partition from that popup menu? I can't remember what was enabled or not, but you did have to select a partition format to get anywhere.