Em 12/07/2015 10:03, "Mick" <michaelkintzios@gmail.com> escreveu:
>
> On Sunday 12 Jul 2015 13:35:25 Marc Joliet wrote:
> > Hi,
> >
> > I have to failed drives that I want to give away for recycling purposes,
> > but want to be sure to properly clear them first.  They used be part of
a
> > btrfs RAID10 array, but needed to be replaced (with "btrfs replace").
(In
> > the meantime I converted the array to RAID1 with only two drives.)
> >
> > My question is how precisely the disks should be cleared.  From various
> > sources I know that overwriting them with random data a few times is
> > enough to render old versions of data unreadable.  I'm guessing 3 times
> > ought to be enough, but maybe even that small amount is overly paranoid
> > these days?
> >
> > As to the actual command, I would suspect something like "dd
> > if=/dev/urandom of=/dev/sdx bs=4096" should suffice, and according to
> >
https://wiki.archlinux.org/index.php/Random_number_generation#.2Fdev.2Furan
> > dom, /dev/urandom ought to be random enough for this task.  Or are
cat/cp
> > that much faster?
> >
> > Any thoughts?
> >
> > Greetings
>
> I use urandom a couple of times (3 to 5), because random takes too long
and I
> don't store state secrets on my disks.  Then I dd onto it a final round of
> /dev/zero.  Finally, run hdparm to securely erase it for good
measure.[1]  All
> of this could be an overkill, but do it out of habit these days.
>
> It is worth saying that I use haveged to increase entropy:
>
> [I] sys-apps/haveged
>      Available versions:
>             1.5
>        ~    1.7a
>             1.7a-r1
>        ~    1.9.1
>      Installed versions:  1.7a-r1(12:46:23 04/21/14)
>      Homepage:            http://www.issihosts.com/haveged/
>      Description:         A simple entropy daemon using the HAVEGE
algorithm
>
> I should clarify that disks which contained financial data are dealth
with a
> high speed angle grinder, after I remove the outer casing of the drive
and don
> a pair of goggles.[2]  *Only then* do I recycle the bits left.  ;-)
>
>
> [1] https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase
>
> [2] You can also use a hammer, a drill, or any similar implement which
will
> completely break the physical disk platters to bits.
>
> --
> Regards,
> Mick

A physical damage is what I guess be the best choice for sensitive data.

I use to disassemble the HDD and rub a strong magnet over the disks'
surfaces.

Just my 2c.

Best regards,
Francisco