[clue] secure erase techniques?

[chris fedde]

It might be a good idea to switch to /dev/zero.  It is much faster
than /dev/random
You need to wait for it to finish to overwrite the whole disk.  As a
least upper bound on the run time take the disk size and divide by the
advertised transfer rate of the interface.  300Gbyte = 300*1024^3,
3Mbyte/sec ideal SATA speed = 3*1024^2

using bc -l

(300*1024^3)/(3*1024^2)
102400.00000000000000000000
./3600
28.44444444444444444444

about 29 hours if you really get full bandwidth from your sata port.
Chances are that's a gross under estimate.

Here is a quick device timing test:

[cfedde at home]$ dd if=/dev/urandom of=/dev/null bs=4096 count=1000
1000+0 records in
1000+0 records out
4096000 bytes (4.1 MB) copied, 0.532551 seconds, 7.7 MB/s

[cfedde at home]$ dd if=/dev/zero of=/dev/null bs=4096 count=1000
1000+0 records in
1000+0 records out
4096000 bytes (4.1 MB) copied, 0.001732 seconds, 2.4 GB/s

/dev/zero is much faster than /dev/urandom

On Wed, Jun 1, 2011 at 9:07 AM, Mike Bean <beandaemon at gmail.com> wrote:
> No harm, no foul, it's not a particularly fast Celeron, so I don't mind
> letting it run long, I just wasn't sure what to expect.
>
> On Wed, Jun 1, 2011 at 8:15 AM, Will <will.sterling at gmail.com> wrote:
>>
>> I should have recommended /dev/zero instead of /dev/urandom.  For your
>> purposes it would have been just as good and faster.
>>
>> On Wed, Jun 1, 2011 at 8:02 AM, Will <will.sterling at gmail.com> wrote:
>>>
>>> It should eventually quit on its own.  The amount of time it will take is
>>> dependent on how fast your CPU can generate random numbers and how large the
>>> partition is.
>>>
>>> On Wed, Jun 1, 2011 at 5:09 AM, Mike Bean <beandaemon at gmail.com> wrote:
>>>>
>>>> How long would I need to leave this running?   cat /dev/urandom >
>>>> /dev/sda1 's been going for long about 10 hours now.  Is this something that
>>>> I'll need to abort or does it terminate on its own?
>>>>
>>>> On Tue, May 31, 2011 at 9:04 AM, chris fedde <chris at fedde.us> wrote:
>>>>>
>>>>> Raymond,
>>>>>
>>>>> What does the magic block size do?
>>>>>
>>>>>
>>>>> I'd go with two passes of "cat /dev/urandom > /dev/sdX" as root.
>>>>>
>>>>> On Tue, May 31, 2011 at 8:51 AM, Raymond DeRoo <rderoo at deroo.net>
>>>>> wrote:
>>>>> > Mike--
>>>>> >
>>>>> > In short, I'm giving one of my older PC's to a friend's friend.  One
>>>>> > of
>>>>> > those, I don't need it, things.  In any case, in terms of secure
>>>>> > destruction
>>>>> > of drives, my father's always taught me to disassemble the drives and
>>>>> > throw
>>>>> > the heads and the platter out separately.  Can't do it here, they
>>>>> > need the
>>>>> > drives, so I thought I'd ask for advice in case we have members who
>>>>> > might
>>>>> > know a thing or two about this sort of thing.  I figured I'd probably
>>>>> > just
>>>>> > boot it to a live CD and nuke the partitions, and that's probably
>>>>> > enough,
>>>>> > after all, I don't need like a military-grade erase, but I'll settle
>>>>> > for
>>>>> > making it @#$@#$@$ hard to recover.  Any suggestions are welcome.
>>>>> >
>>>>> >
>>>>> > # dd if=/dev/urandom of=/dev/sda bs=387 count=<size of disk in bites>
>>>>> > / 383
>>>>> > Recover from this *IS* still possible, but generally requires someone
>>>>> > who is
>>>>> > *VERY* knowledge about drives to do as such.
>>>>> > .r
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