SSD & Disk erase

Tech198

macrumors G5
Original poster
Mar 21, 2011
14,057
1,668
Australia, Perth
Can a secure erase be done ok on SSD? or would it amount to 'wear leveling' ?

The option is greyed out in OS X Utilities (when booted from install media)


Also information in relation to certain data (maybe not personal, i dunno), but once its on there, it remains there indefinably.

Aside from the performance benefit, this makes me wanna go back to using hard drives..


Anyone have any experiences with this ?
 

CyBeRino

macrumors 6502a
Jun 18, 2011
732
26
Doing a secure erase on an ssd is a fairly bad idea because first of all it writes to all sectors that are available to the OS, perhaps even multiple times depending on erase settings, and it doesn't actually erase everything on the drive because of the wear leveling algorithms and overprovisioning.

Most SSDs however encrypt data before storing it in flash, so with the right tools you can do a real secure erase on an SSD in no time because they just erase the encryption key instead, making all the data on there completely unreadable.
 

Tech198

macrumors G5
Original poster
Mar 21, 2011
14,057
1,668
Australia, Perth
Most ?

Is there any details of this ? or only on the high end SSD's ?

In any case, Apple should made "Secure erase" in the GUI available of DU, but since they can detent he presence of a SSD drive, Apple should just erase the "pointers", very similar how when you "ease all content and settings" on iPhone 3gs/iPad and later.

http://support.apple.com/kb/ht2110
 

maflynn

Moderator
Staff member
May 3, 2009
63,988
30,532
Boston
I think secure erasing is not needed on SSDs and only causes unnecessary wear and tear on the SSD.

What is secure erase? Well remember for on hard drives, erasing a file or folder does not remove the actual data just the reference to the data. You can, with the right software, get the data back. Additionally because its magnetic, there is software that can reconstuct the data because of the trace magnetic information that remains.

Fast forward to modern SSDs and they when an erase occurs, the data is actually removed. The state of the SSD memory is changed and there's no trace magnetic information to recover. To put it another way, erasing files/folders on SSDs is destructive and a secure erase isn't needed.

Edit:
Caveat, SSDs that don't have garbage collection or you don't have TRIM enabled mean that the data on the SSD isn't removed at deletion time
 
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Weaselboy

Moderator
Staff member
Jan 23, 2005
29,295
8,944
California
Can a secure erase be done ok on SSD? or would it amount to 'wear leveling' ?

The option is greyed out in OS X Utilities (when booted from install media)


Also information in relation to certain data (maybe not personal, i dunno), but once its on there, it remains there indefinably.

Aside from the performance benefit, this makes me wanna go back to using hard drives..


Anyone have any experiences with this ?
If you are concerned about this you can encrypt the SSD with OS X included Filevault2 encryption, then boot from a USB key or Internet recovery and erase the encrypted drive. This way even if someone did somehow manage to even partially restore the erased drive, anything on it would still be encrypted and completely inaccessible.
 

cal6n

macrumors 68000
Jul 25, 2004
1,935
24
Gloucester, UK
If you reformat your SSD using Disk Utility and then leave it powered up in your system, then the SSD's garbage collection process should kick in automatically. As I understand it, this goes through the drive, setting each bit that's been declared usable to zero individually and then making each one writable, effectively deleting your data in a reasonably secure manner. Unfortunately, I don't know of any way to monitor its progress while it's doing this.
 
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Fishrrman

macrumors P6
Feb 20, 2009
17,384
5,622
The "state of the art" insofar as drive maintenance and utility apps goes, has yet to "catch up" with the technology of SSD's.

What's needed is a drive utility specifically designed to maintain and manipulate SSD's...