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So I have a Seagate 2TB bare drive in an external enclosure as my Time Machine backup drive. It has been acting up and giving SMART errors. I decided I should RMA or replace it before it dies altogether, but I'm concerned about the data still on it. My choices are:

  1. Use Disk Utility to securely erase the drive
  2. Boot with DBAN and do basically the same thing
  3. Buy a new drive and physically destroy the old one
  4. ...

I'm leaning towards 3, because some of the client data I have have on the drive is quite sensitive. I'm not paranoid about it, but I'd like to be able to say no corners were cut to ensure the data is secure.

But I've been reading up on secure erasing and came across this utility CMRR Secure Erase which looks pretty good. The utility I can't get working on the computers I have available to me right now. It's also unsupported.

I tried to manually fire up the Secure Erase function by connecting the drive to a linux computer and used the command

sudo hdparm --security-erase-enhanced bob /dev/sdb

But while the command was issued, it didn't seem to take. I waited a while then reconnected it back to the Mac and the files were still there.

So I was wondering if there was any way to access a drive's Secure Erase function on a Mac or Linux computer?

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3 Answers 3

Apparently you need to set a master password before issuing the SECURITY ERASE UNIT command. You could try following the instructions here.

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You know, this is exactly what I was looking for, but I couldn't get my Ubuntu computer to actually execute the commands -- it would fail each time. I +1'd you for the answer even though I ended up just zeroing the disk out using Disk Utility on the Mac. –  emgee Nov 19 '09 at 4:45

Mac OS X's built-in secure erase is good enough for general use -- the only thing it'll really miss is bad blocks that've been mapped out (since they're mapped out, it can't write over them, so they'll still contain whatever they held when they were mapped out). If you're paranoid, I recommend following the erase with a check to make sure the disk's actually blank. You can do this from the OS X command line like this:

sudo diskutil zeroDisk /dev/disk1
sudo od -x /dev/disk1

(replacing /dev/disk1 with the correct device, obviously. Zeroing the wrong disk would be bad.) The key is that the od command should print something like this:

0000000      0000    0000    0000    0000    0000    0000    0000    0000
*
606600000

The important part is the "*", meaning "more of the same" -- if it prints anything other than zeroes, the asterisk, and addresses (in the left column), the disk isn't fully blank. Note that you can only usefully perform this test right after using the zeroDisk function -- not, for example, an erase in Disk Utility, 'cause that'll immediately reformat the disk, and so it won't still be zeroed when you go to check.

BTW, OS X also offers some "even more secure than zeroing" options: a 7-pass DOD-spec-based erase, and a 35-pass Guttman algorithm erase. The additional erase passes don't actually do anything useful on modern hard disks, so I'd just go with zeroing. (Note: if you were talking about an SSD, it'd be different.)

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If you care so much to ask about it, erase it in software, then destroy it physically. Data recovery companies can do miracles if well paid.

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