[ale] erasing a hard drive

[Jim Kinney]

Dd if=/randomladygaga.mp3 of=/dev/sda
On Aug 26, 2011 3:15 PM, "Lightner, Jeff" <JLightner at water.com> wrote:
> Yep - I started using /dev/urandom instead of /dev/zero when I read
something that said if the overwrite data is predictable (e.g. all zeros) it
might be easier to decide what real data it was trying to mask.
>
>
>
>
>
> -----Original Message-----
> From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of David
Tomaschik
> Sent: Friday, August 26, 2011 2:52 PM
> To: Atlanta Linux Enthusiasts
> Subject: Re: [ale] erasing a hard drive
>
> On Fri, Aug 26, 2011 at 1:37 PM, Lightner, Jeff <JLightner at water.com>
wrote:
>> Of course you don't need a software at all.
>>
>> Erasing the data in a filesystem then unmounting the filesystem and
running:
>> dd if=/dev/urandom of=/dev/sda1/scramble bs=1M
>>
>> - will write random data on the partition (sda1 in the above - you can
substitute other partitions/drive letters as necessary)
>>
>> However, any time I've seen this question come up someone invariably
posts that it really isn't necessary for "modern drives". They never quite
say what their definition of "modern" is.
>>
>> In the past it was required to do something like the above multiple times
but it really isn't necessary unless you're doing DOD or CIA work.
>
> It is necessary to do at least one overwrite pass. Recovering data
> from a drive that has not been overwritten at all (e.g., mkfs or rm
> only) is trivial.
>
> The theory behind multiple overwrites has to do with the fact that
> data isn't really stored in discrete chunks on the drive, and there
> are algorithms that can theoretically recover/rebuild data from the
> "edges" of the tracks. However, this is substantially less of an
> issue these days. For one, those techniques were developed against
> MFM and RLL encoded drives. Drives using PRML and EPRML and
> perpendicular recording are believed to be far more resistant to this
> (as they have less area in which other traces are left.)
>
> For a better explanation than I could write, see
> http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html (especially
> the epilogue).
>
>
> --
> David Tomaschik, RHCE, LPIC-1
> System Administrator/Open Source Advocate
> OpenPGP: 0x5DEA789B
> http://systemoverlord.com
> david at systemoverlord.com
>
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