Secure Erase of Hard Disks

TidBITS Talk
21

According to the article I cited, this was apparently the case in the 80’s and early 90’s in the days of MFM and RLL drives with stepper motors and such. But the technologies used in modern hard drives (PRML and SMR encoding, and incredibly high data densities) make it far more difficult to try and read underneath erased data, even with a single-pass-zero erasure.

The author says that although it may be possible to extract a few bits of data, extracting whole bytes (let alone files) is pretty much impossible. The author has an outstanding request to the data forensics community for any information to the contrary but (in 2012, when the article was written) had not received any such information.

I do agree that if you have data of extreme sensitivity, then “better safe than sorry” and go for data destruction. But I think that’s for peace of mind, not because of a legitimate concern.

Physical destruction is also important if the drive is broken. If you can’t actually run an erase cycle, then you need to degauss or shred or otherwise destroy the device, since platters can be transplanted into other devices for data recovery purposes. (See also https://www.youtube.com/watch?v=J9P4UadRdNA )

And SSDs are another topic, but if people want to discuss that, I’d rather it be done on another thread (and it has already been discussed many times before).

I’m not too surprised. Resellers are all afraid of being held liable if someone buys the drive and manages to recover sensitive data. It’s easier to just refuse to resell the drive than to take the time to erase the entire contents.

Note that you can’t magnetically bulk-erase a modern hard drive, because that will blow away the low-level format, which can’t be re-recorded without special equipment that is generally not found outside of the factory. Back in the old days of MFM/RLL drives, you could bulk-erase it and then re-apply a low-level format, but that is impossible on all but the most ancient drives.

But it’s also due to the fact that HDDs are so inexpensive these days that there is rarely a reason for anyone to buy a used one. And without a significant resale market, there’s little reason for anyone to buy one.

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Could be…this was back in 1990 or so and the higher density drives now that work differently might not be able to be done so…and as I said it was only bits and pieces of things, not an entire Word document. Me…I figure hard drives are cheap enough and I’ve used them long enough before replacing them that they’re getting to EOL anyway so I destroy them.

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FWIW - I leave the drives in a box for a few years until its even less likely that any data will be of any use (not as a security protocol, just because I’m lazy) - then I take them apart, which is trivially easy in most cases; mainly to extract the extremely powerful magnets they contain. I find these incredibly useful. We happen to have a shredder which also does CDs; so if I can be bothered, I then put the platters through that (or use them as coasters). But mainly I take a few drives apart when I need some more magnets!

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I have a bunch of the WD USB powered 4 TB drives. It takes about 14 hours to secure erase these drives (2-pass - the lowest secure option in Disk Utility). I have been running the secure erase on two systems running 24 hrs a day. Almost done, I am going to donate these drives and I hope they can be reused but in any event I know they are cleaned up. Thanks again for the many helpful comments in this thread,.

David

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I’m surprised that works, since HDD platters are usually metal or glass. I’d expect to need a shredder designed for the purpose.

That having been said, once the platters are removed, data destruction is easy. Any strong abrasive (e.g. sandpaper) should easily be able to remove the magnetic coating. And if the platters are glass (used in many 2.5" drives), they can also be shattered with a hammer (put it in a bag if you do this to avoid getting shards all over the place).

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In my experience having disposed of glass plattered hard drives in this way, hard, extremely sharp shards, so definitely pay attention to David’s warning.