secure erase free space on SSHD

Question

Level 1

23 points

secure erase free space on SSHD

I have a 500Gb Toshiba SSHD installed inside my MacBook as a replacement startup drive. Using Disk Utility I have tried to erase/overwrite the free space on this HD. The "Erase Free Space" button is grayed out and hovering gives the following message: "Erasing free space not available on this type of drive".

Is there anything I can safely do to erase free space? Since I have deleted a large number of files from the HD to free up space for future work, I am just trying to be security conscious.

An aside: I have wondered if with a SSHD there is less or even no need to erase free space as there might be no residue in the memory locations to permit recovery like there is with a conventional HD, but this is speculation on my part.

Thanks, John

MacBook (13-inch Mid 2010), OS X Mountain Lion (10.8.5)

Posted on Feb 28, 2015 10:46 AM

Reply

Answer 1

Niel

Level 10

726,749 points

Feb 28, 2015 10:47 AM in response to fusodrvr

Deleting the data normally made it difficult to recover. You don't need to do anything else.

(123258)

Reply

Answer 2

fusodrvr Author

Level 1

23 points

Feb 28, 2015 10:50 AM in response to Niel

Niel

Thanks for the reply!

So, even if some of the normally deleted files [normal empty trash] were financial files with sensitive information, I need not worry? Or is it that I have 'reduced' the recoverability?

If the latter, is there a way to do more, or is that the best I can do with this type of HD?

Thanks.

Reply

Answer 3

Niel

Level 10

726,749 points

Feb 28, 2015 10:52 AM in response to fusodrvr

That's the best you can do with them. For future cases, encrypt documents which contain sensitive data; the Disk Utility can be used to create an encrypted disk image, and you can turn on FileVault.

(123260)

Reply

Answer 4

fusodrvr Author

Level 1

23 points

Feb 28, 2015 10:57 AM in response to Niel

Thanks again.

I did have the financial files stored inside an encrypted 'xxx.sparse.image' partition on the HD. I erased and deleted the partition, and then created a new one for future use. I guess that's the best I can do.

again, thanks for your very prompt replies.

Reply

Answer 5

BobHarris

Level 9

53,009 points

Feb 28, 2015 2:04 PM in response to fusodrvr

A Solid State Device never writes to the same place that you read the data from. The SSD hardware logic always allocates a new pre-cleared sector and writes to that sector, and the hardware maps that sector to the logical offset for the previous sector. The previous sector is released to the SSD hardware to be pre-cleared at some future time for reuse as a place to write.

So zeroing SSD storage just reduces the life of the drive without actually zeroing the data you desire.

If Mac OS X is detecting that your SSHD has an SSD component, it will not do anything to shorten the life of the SSD component by doing things that are not doing what you expect (aka securely erasing data, which the SSD will NOT be doing).

If you are using an SSD type device, the ONLY way to make sure deleted files are secure after deletion is to enable FileVault so that the entire disk is ALWAYS encrypted so that deleted files are just random bits to anyone trying to access the data without the disk encryption keys.

Reply