I have two G-Drive 6TB Hard Disks that I have been using for backup. I am moving to all SSD drives and will donate these drives - and want to make sure all the data is unreadable. In the past I have done a secure erase - but that takes a long time for these large hard disk drives. So, this time I figured I would encrypt the drives, then erase and reformat - nothing would be readable after that. But, the encryption process has been running for 18 hours and it doesn’t look like much has actually been encrypted. (I am running MacOS 15.2 on a Mac Studio.) So, it looks like this process is even slower than a secure erase. Has anyone had experience with encrypting these large hard disks? (There is 5 TB of data on the 6TB drive.) I am wondering if I should just stop the encryption and revert to the secure erase.
When I have run a Finder Encrypt command, I remember it taking a day or so. I think it was on a 8 Tb drive. Not sure if having the Finder in the forefront makes it happen faster.
If the purpose is to wipe the drive for resale/donation, the encrypt method is time consuming overkill. Changing/losing the enrcryption key is a fast easy method if the data has been encrypted all along. But if that’s not the case, I wouldn’t do it that way.
If your drive (and its enclosure, if it’s external) supports a secure-erase mechanism (e.g. the SATA 3 “SANITIZE” command or the older ATA “Security Erase” command, the SCSI/UAS “FORMAT UNIT” command or PCIe/NVMe’s “FORMAT NVM” command). This should tell the the drive hardware to securely erase everything using a mechanism the manufacturer considers appropriate, including normally-inaccessible regions like the pool of blocks marked as bad or spare. I know of free software for Windows and Linux that can issue these commands but I don’t know of a Mac utility for this.
If you can’t issue a secure-erase command directly to the drive, then my recommendation is to perform a fairly generic one-pass erase command (write zeros to every block). For example, one of the following commands (after unmounting every volume on the disk):
$ diskutil zeroDisk /dev/disk###
$ disktuil randomDisk /dev/disk###
Where disk### is the media’s device name (e.g. /dev/disk5). Make sure you don’t provide the wrong device name, or you’ll end up wiping stuff you want to keep and will have to recover by restoring from a backup and/or reinstalling macOS.
You could also use the diskutil secureErase command and select one of the multi-pass algorithms, but I think that is unnecessary overkill. The goal of those is to try and scramble the magnetic signature to eliminate any hints about what might have previously been recorded. But I’ve never read any paper showing actual data recovery from this, only theoretical papers describing how it might be possible. And those are all from the days of MFM/RLL hard drives, where software could access the raw magnetic bit-patterns. With modern hard drives, even the authors of those original papers say it’s not possible.
Ditto for those who talk about data recovery using a magnetic force microscope. Although researchers have seen magnetic after-images on erased media, I have never seen a single document describing actually recovering files from those after-images.
In other words, if your data is so sensitive that you think you can’t trust a simple one-pass wipe with zeros or random values, then you shouldn’t trust anything and should physically destroy the device.
I also remember that I could not figure out a way to get it to stop encrypting once I started it. Will those command lines stop it if it is already encrypting?
I’m not sure. It was my experience that the FileVault software can’t change the status of a drive while encryption/decryption is in progress.
When, several years ago, I tried to use it to encrypt a laptop drive and found that it wouldn’t complete after several days, I couldn’t stop it. I ended up wiping the computer and restoring from a backup in order to make it stop.
Now in the case of an external drive, you might have better luck. If you unmount its volumes and then wipe the drive (not its volumes), that should clobber the partition table and all of the per-volume file system structures. Hopefully that should wipe whatever macOS uses to record the encryption state as well.
The first drive completed this morning - about 40 hours in total I think. The second drive is still running.
These drives were not encrypted originally - if they had, it would be easy to erase and throw away the key. But I don’t encrypt my external backup drives because they don’t leave home and are stored in a locked fire safe. (I understand “best practice” is to store of-site copies, but I never thought that was necessary.)
Thanks for the comments.
David
If anyone is able to read them, it will be government organisations. If they are interested with what is on your disks then you will have much greater problems, and they have a lot easier ways to find out.