Question on shredding a terebyte drive

[Robin Laing]

Dean S. Messing wrote:
> Thanks to all for the replies.
> 
> I'll answer most of the comments here.
> 
> 0) The disk is unmounted.
> 
> 1) The drive is (was) a backup drive with a great deal of sensitive
>    corporate laboratory research data and algorithms on it.  The
>    monitary loss of the data being stolen would be significant though
>    it's hard to put a $$ value on it.  More importantly, I'm following
>    corporate policy.
> 

This is the most problematic issue.  Corporate policies that were 
written when drive sectors were visible with a home microscope.

That said, I would go with the dd recommendations, 25 times.

Also, the -v option will slow the progress due to screen writes.  I have 
seen this in the past.

And, if the drive is mounted as ext3, then the data may not get erased 
as expected.  See the man page on shred.

CAUTION:  Note that shred relies on a very important assumption:
        that the file system overwrites data in place.  This is the tra-
        ditional  way  to do things, but many modern file system designs
        do not satisfy this assumption.  The following are  examples  of
        file  systems on which shred is not effective, or is not guaran-
        teed to be effective in all file system modes: ...

Again, dd gets around this.

As for the comments on the "secure erase" features of drives.  A quick 
google search came up with:

http://ata.wiki.kernel.org/index.php/ATA_Secure_Erase
Which shows how to use hdparm.

http://advosys.ca/viewpoints/2006/07/hard-drive-secure-erase/
Which is a very interesting article and this is really important.

We tried the secure erase utility on multiple old ATA drives and every 
one manufactured since 2000 supported the Security Erase command (the 
utility tells you if the drive does not). Drives older than 2000 don’t 
have the command so if you need to wipe very old drives, a software wipe 
is the best you can do.

Maybe run the secure erase 25 times.


-- 
Robin Laing