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#45800 - 07/24/17 02:55 PM Erasing or over-writing an external SSD?
Pendragon Offline


Registered: 08/04/09
Loc: Georgetown, Texas, USA
I have an external OWC SSD (partitioned) that is/was used as a backup for a 2011 MacBook Pro.

The logic board crashed today (per the Genius) and Apple won’t fix it because it is a “legacy” device. I'm guessing the MBP is probably not worth with a commercial fix.

I would now like to use the OWC SSD as a backup for my wife’s machine, but I don’t know if I should first erase the SSD or merely allow Carbon Copy Cloner to over-write what’s there. confused

Waddya think?
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Harv
27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45801 - 07/24/17 03:50 PM Re: Erasing or over-writing an external SSD? [Re: Pendragon]
artie505 Online


Registered: 08/04/09
Has your wife got security clearance? tongue

In theory, erasing an SSD accomplishes little more than shortening its life.

One way or another, your data will still be on the drive in some way, shape, or form...recoverable by anyone with the desire and means.
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45803 - 07/24/17 04:37 PM Re: Erasing or over-writing an external SSD? [Re: artie505]
Pendragon Offline


Registered: 08/04/09
Loc: Georgetown, Texas, USA
Since the data on the SSD is of little consequence, I fear not should it eventually be recovered. That being the case, I presume the "over-write" approach is the better option. But is that a safe presumption?
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Harv
27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45804 - 07/24/17 04:49 PM Re: Erasing or over-writing an external SSD? [Re: Pendragon]
artie505 Online


Registered: 08/04/09
Originally Posted By: Pendragon
Since the data on the SSD is of little consequence, I fear not should it eventually be recovered. That being the case, I presume the "over-write" approach is the better option. But is that a safe presumption?

"Erase" is counterproductive...even more-so for non-critical data, so "overwrite" is really your only option.

But will cloning your wife's installation to the SSD completely overwrite what's already on it is a question for others to answer.
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45817 - 07/25/17 07:10 AM Re: Erasing or over-writing an external SSD? [Re: artie505]
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
Originally Posted By: artie505
But will cloning your wife's installation to the SSD completely overwrite what's already on it is a question for others to answer.

Given sufficient time, money, and desire to obtain the contents of an erased (overwritten) drive, be it SSD or Rotating media the only absolute way to guarantee the data cannot be recovered is to mechanically destroy the drive. (Think of Frodo, with the unintentional help of Golem, casting the one ring into the volcanic fire from which it was made.)

But, as a practical matter, the data would be so difficult (read EXPEN$IVE) to retrieve in a coherent form the malefactor would have to be convinced there was data worth the cost of retrieval before they would be likely to attempt it. So unless Pendragon's wife has information the disclosure of which is likely to cause GRAVE damage to the security of the nation or a multi billion dollar institution on her drive just overwriting the data would seem a reasonable risk.

NOTE: With APFS in High Sierra (even without encryption) the recovery task becomes immensely more difficult.
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#45819 - 07/25/17 08:43 AM Re: Erasing or over-writing an external SSD? [Re: joemikeb]
Pendragon Offline


Registered: 08/04/09
Loc: Georgetown, Texas, USA
Many thanks Artie & Joe.

I now fully understand the situation and am comfortable with what I have learned. The CIA & NSA and such are not likely to call, but I believe I now know enough to quell the need of common users.
_________________________
Harv
27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45870 - 07/30/17 02:54 PM Re: Erasing or over-writing an external SSD? [Re: Pendragon]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
There is one advantage to erasing it (note: do not use a security erase or overwrite what's there; that results in SSD wear):

Your old MacBook Pro almost certainly did not use TRIM on the SSD. That means the SSD would have been forced to use its own garbage collection, which over time will cause the SSD to become slower and slower at writing information, for various complicated reasons related to the peculiar way NAND flash records data. Erasing the drive will reset the garbage collect, returning the drive to its original speed.
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#45877 - 07/31/17 05:36 AM Re: Erasing or over-writing an external SSD? [Re: tacit]
Pendragon Offline


Registered: 08/04/09
Loc: Georgetown, Texas, USA
Originally Posted By: tacit
There is one advantage to erasing it (note: do not use a security erase or overwrite what's there; that results in SSD wear):

Your old MacBook Pro almost certainly did not use TRIM on the SSD. That means the SSD would have been forced to use its own garbage collection, which over time will cause the SSD to become slower and slower at writing information, for various complicated reasons related to the peculiar way NAND flash records data. Erasing the drive will reset the garbage collect, returning the drive to its original speed.


Tacit,

I’m still a bit confused…

When you say do not use a security erase or overwrite, that I understand. But then, how should I erase the drive? Do you mean a simple erase via Disk Utility or what? confused
_________________________
Harv
27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45880 - 07/31/17 10:37 AM Re: Erasing or over-writing an external SSD? [Re: Pendragon]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
Exactly. Just a simple erase.
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Photo gallery, all about me, and more: www.xeromag.com/franklin.html

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#45881 - 07/31/17 10:43 AM Re: Erasing or over-writing an external SSD? [Re: tacit]
Pendragon Offline


Registered: 08/04/09
Loc: Georgetown, Texas, USA
Merci, mon ami.

Clearly, some of us are a tad slower/duller than others. Well, alright, a big tad...
_________________________
Harv
27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45882 - 07/31/17 10:50 AM Re: Erasing or over-writing an external SSD? [Re: Pendragon]
grelber Offline


Registered: 08/05/09
Loc: North of 49th ||
Originally Posted By: Pendragon
When you say do not use a security erase or overwrite, that I understand. But then, how should I erase the drive? Do you mean a simple erase via Disk Utility or what? confused

I'm not sure if it'll help, but when I finally junked my iMac DV SE running Mac OS 9 (which had install disks), I simply booted from the install disk, choose Disk Setup, erased the entire hard drive (a mere 15 GB) first then overwrote it all with zeros (which took 2 hours!), reinstalled basic Mac OS 9 and deleted all apps and files associated with same.
Since there was nothing truly worth retrieving in all that was erased, I felt safe enough consigning it to a government-approved electronics recycler; it'll still probably wind up on a beach in Somalia.

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#45885 - 07/31/17 03:35 PM Re: Erasing or over-writing an external SSD? [Re: grelber]
artie505 Online


Registered: 08/04/09
Originally Posted By: grelber
I'm not sure if it'll help, but when I finally junked my iMac DV SE running Mac OS 9 (which had install disks), I simply booted from the install disk, choose Disk Setup, erased the entire hard drive (a mere 15 GB) first then overwrote it all with zeros (which took 2 hours!)....

Your first step erased your directory, but it left your data intact, and it's what Harv should do.

The zero overwrite, i.e. secure erase, is contraindicated for SSDs.
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45887 - 07/31/17 04:29 PM Re: Erasing or overwriting an external SSD? [Re: artie505]
grelber Offline


Registered: 08/05/09
Loc: North of 49th ||
Originally Posted By: artie505
Your first step erased your directory, but it left your data intact ...

I left out the in-between step whereby I initialized the entire drive thereby destroying all the data files. The zero overwrite was just added 'protection'.

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#45888 - 07/31/17 04:50 PM Re: Erasing or overwriting an external SSD? [Re: grelber]
artie505 Online


Registered: 08/04/09
Originally Posted By: grelber
Originally Posted By: artie505
Your first step erased your directory, but it left your data intact ...

I left out the in-between step whereby I initialized the entire drive thereby destroying all the data files. The zero overwrite was just added 'protection'.

How did you do that in-between step?
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45891 - 08/01/17 12:09 AM Re: Erasing or overwriting an external SSD? [Re: artie505]
grelber Offline


Registered: 08/05/09
Loc: North of 49th ||
Originally Posted By: artie505
Originally Posted By: grelber
Originally Posted By: artie505
Your first step erased your directory, but it left your data intact ...

I left out the in-between step whereby I initialized the entire drive thereby destroying all the data files. The zero overwrite was just added 'protection'.

How did you do that in-between step?

Nothing tricky. Checking through the possible subroutines for Disk (or Drive) Setup (on the Mac OS 9 Install CD) I found the option to initialize the entire drive; so I choose it and actually ran it twice.

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#45893 - 08/01/17 12:46 AM Re: Erasing or overwriting an external SSD? [Re: grelber]
artie505 Online


Registered: 08/04/09
Originally Posted By: grelber
Originally Posted By: artie505
Originally Posted By: grelber
Originally Posted By: artie505
Your first step erased your directory, but it left your data intact ...

I left out the in-between step whereby I initialized the entire drive thereby destroying all the data files. The zero overwrite was just added 'protection'.

How did you do that in-between step?

Nothing tricky. Checking through the possible subroutines for Disk (or Drive) Setup (on the Mac OS 9 Install CD) I found the option to initialize the entire drive; so I choose it and actually ran it twice.

There's no way I've ever heard of to "destroy all the data files".

You can't "destroy" your files; the best you can do is overwrite them with zeros once or more, as you did, but I'm pretty sure that initializing a drive doesn't do that. It's a pretty quick process as I recall...more along the lines of, if not precisely, a simple erase.
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45894 - 08/01/17 01:55 AM Re: Erasing or overwriting an external SSD? [Re: artie505]
grelber Offline


Registered: 08/05/09
Loc: North of 49th ||
Originally Posted By: artie505
There's no way I've ever heard of to "destroy all the data files".

You can't "destroy" your files; the best you can do is overwrite them with zeros once or more, as you did, but I'm pretty sure that initializing a drive doesn't do that. It's a pretty quick process as I recall...more along the lines of, if not precisely, a simple erase.

Maybe yes, maybe no. As far as I'm concerned, I "nuked" the hard drive sufficient to my purposes (especially given lack of concern for the sensitivity of the data thereon).

Perhaps someone more au courant on the subject (such as tacit or joemikeb) could chime in here.

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#45895 - 08/01/17 01:59 AM Re: Erasing or overwriting an external SSD? [Re: grelber]
artie505 Online


Registered: 08/04/09
It was the zeros that did the job, but the point of this discussion is that zeros are no longer a useful option.
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#45896 - 08/01/17 02:08 AM Re: Erasing or overwriting an external SSD? [Re: artie505]
grelber Offline


Registered: 08/05/09
Loc: North of 49th ||
Originally Posted By: artie505
It was the zeros that did the job, but the point of this discussion is that zeros are no longer a useful option.

I just noticed that today's Dilbert is quasi on point:
"When you delete software, where do all the zeroes and ones go?"

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#45897 - 08/01/17 07:48 AM Re: Erasing or overwriting an external SSD? [Re: grelber]
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
Originally Posted By: grelber
I just noticed that today's Dilbert is quasi on point:
"When you delete software, where do all the zeroes and ones go?"

The bit bucket of course cool — at least that was what we used to say back in the 60s and 70s.

Originally Posted By: grelber
Nothing tricky. Checking through the possible subroutines for Disk (or Drive) Setup (on the Mac OS 9 Install CD) I found the option to initialize the entire drive; so I choose it and actually ran it twice.

Back in the pre-IDE (Integrated Drive Electronics) / ATA (Advanced Technology Attachment) days Initializing a drive included low level disk formatting such as writing sector boundaries on the drive media as well as creating an empty directory structure on the drive.

With the advent of IDE/ATA that low level formatting became the responsibility of the IDE and Initializing a drive was reduced to creating a partition table/map and an empty volume file directory the assumption being the low level formatting has already been taken care of by the IDE.

Today erasing a drive implies rewriting the drive partition table and creating an empty file directory for the volume on the drive. Erasing a volume creates an empty file directory for that volume.

In none of these cases is the data actually erased or overwritten, the only thing changed is the Directory or the Directory and partition table. Therefore it is possible, with some effort, to recover files from a drive or volume that has been initialized or erased. In fact that is how the various file recovery apps that were so popular some years ago were able to recover any files.

The Secure Erase option for a drive/volume/file works by overwriting the physical storage location with all zeros or all ones or a combination of those one or more times. With a good enough lab, sensitive equipment, time, skill, and money it is possible to read ghost images of previous magnetic impressions on rotating media. Generally a 7x overwrite is considered secure enough erasure for all but the most critical security data. For the most sensitive material the requirements call for mechanically reducing the media to the consistency of course sand.

Solid State media is another bag of worms and when you add to that APFS formatting, reconstructing the data becomes far more complex. If on top of that the volume was encrypted it is arguably as secure as magnetic media that has been securely erased, even at the maximum number of overwrites.

The level of security you are comfortable with is entirely a personal decision — unless the data belongs to another person/company/institution/government entity. As for me, I have no paranoid tendencies and probably what I do is overkill, but my drives are formatted APFS (Encrypted) or MacOS Extended (Journaled, Encrypted) and as much as possible/practicable my internet communications are end to end encrypted, I regularly use a VPN and sometimes even TOR browser and routing. Frankly I am surprised to find myself at this level of security, but it has evolved over time and one at a time, and so far any performance impact has been unnoticeable, even on my five year old Mac mini.


Edited by joemikeb (08/01/17 08:34 AM)
Edit Reason: Hit return too soon
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#45900 - 08/01/17 04:56 PM Re: Erasing or overwriting an external SSD? [Re: joemikeb]
artie505 Online


Registered: 08/04/09
Thanks for clarifying the various incarnations of "erase".

I used it above in the sense of "delete from the directory", which I think is its most common usage, but after reading your post I'll give thought to being more descriptive in the future.
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