Overwriting a 4096 byte sector harddisk drive with random data

[Michael D. Setzer II]

On 21 Jul 2011 at 20:15, yudi v wrote:

Date sent:	Thu, 21 Jul 2011 20:15:39 +1000
Subject:	Re: Overwriting a 4096 byte sector harddisk drive with random data
From:	yudi v <yudi.tux at gmail.com>
To:	Community support for Fedora users <users at lists.fedoraproject.org>
Send reply to:	Community support for Fedora users <users at lists.fedoraproject.org>
	<mailto:users-request at lists.fedoraproject.org?subject=unsubscribe>
	<mailto:users-request at lists.fedoraproject.org?subject=subscribe>

> 
> 
> 
> On Thu, Jul 21, 2011 at 8:04 PM, Gilboa Davara <gilboad at gmail.com> wrote:
>     On Thu, 2011-07-21 at 19:48 +1000, yudi v wrote:
>     > Hi
> > From what I understand, the first command above will write data in
> > 512 byte blocks, the second one in 1MB blocks, and the third in 
> 4096
> > byte blocks. Right?
> 
>     Yep.
>     The 1M should also yield considerably better performance. 
>     (Though the
>     random number generator may cap the performance in this 
>     case).
>     
>     - Gilboa
>     
>     -
> 
> Sorry, could you please elaborate a bit more on how a higher size block results in better 
> performance.

I maintain a disk imaging project, and bs can make a big 
difference depending on the disk and hardware being used. Here 
is a quick set of test I just did creating a 10MB file from urandom 
on my system. You may get higher or lower results depending on 
your hardware and the size of the file or disk.

time  dd if=/dev/urandom of=test1 bs=1M count=10
10+0 records in
10+0 records out
10485760 bytes (10 MB) copied, 1.23827 s, 8.5 MB/s

real	0m1.241s
user	0m0.000s
sys	0m1.222s

time  dd if=/dev/urandom of=test1 bs=4096 count=2560
2560+0 records in
2560+0 records out
10485760 bytes (10 MB) copied, 1.26018 s, 8.3 MB/s

real	0m1.264s
user	0m0.001s
sys	0m1.241s

time  dd if=/dev/urandom of=test1 bs=512 count=20480
20480+0 records in
20480+0 records out
10485760 bytes (10 MB) copied, 1.3672 s, 7.7 MB/s

real	0m1.371s
user	0m0.002s
sys	0m1.352s






> 
> -- 
> Kind regards,
> Yudi
> 


+----------------------------------------------------------+
  Michael D. Setzer II -  Computer Science Instructor      
  Guam Community College  Computer Center                  
  mailto:mikes at kuentos.guam.net                            
  mailto:msetzerii at gmail.com
  http://www.guam.net/home/mikes
  Guam - Where America's Day Begins                        
  G4L Disk Imaging Project maintainer 
  http://sourceforge.net/projects/g4l/
+----------------------------------------------------------+

http://setiathome.berkeley.edu (Original)
Number of Seti Units Returned:  19,471
Processing time:  32 years, 290 days, 12 hours, 58 minutes
(Total Hours: 287,489)

BOINC at HOME CREDITS
SETI        11023792.670369   |   EINSTEIN     6216520.680851
ROSETTA      3399923.990913   |   ABC          6993668.719655