topic Re: using dd command to zero out disks in Operating System - HP-UX

using dd command to zero out disks

Mark Harshman_1 — Sun, 07 Mar 2004 09:19:55 GMT

i want to zero out a number of disks on a device i am de-commissioning. FOr audit reasons..we are suppose to "zero" out the data. I was thinking of using the "dd" command...but am not sure of the a good syntax? i could use some assistance here...thanks in advance.

Re: using dd command to zero out disks

Donny Jekels — Sun, 07 Mar 2004 09:43:15 GMT

dd if=/dev/null of=/dev/dsk/c0t0d0

Re: using dd command to zero out disks

Hein van den Heuvel — Sun, 07 Mar 2004 10:08:59 GMT

/dev/null will not do.
It returns 'eof' rightaway and your disk blocks will nto be overwritten.

Use

if=/dev/zero bs=1024k

[use search in the forum for more detailed discussion on device scrubbing, /dev/random, torches (the only real way to destroy data :-) and so on.]

hth,
Hein.

Re: using dd command to zero out disks

Mark Harshman_1 — Sun, 07 Mar 2004 10:42:34 GMT

thanks for the answers. is there a way to sting several disks all togther? can i create an input file as my of=? i have over 100 disks i need to wipe.....

thanks

Re: using dd command to zero out disks

Michael Schulte zur Sur — Sun, 07 Mar 2004 10:48:16 GMT

Hi,

you can write the disk devices in a file and let a loop run over it.

dskfile:
/dev/dsk/c0t0d0
/dev/dsk/c0t1d0
...

while read DISK
do
dd if=/dev/zero of=${DISK}
done < dskfile

Michael

Re: using dd command to zero out disks

Hein van den Heuvel — Sun, 07 Mar 2004 11:43:19 GMT

With a hunderd disk, you want to write more than one at a time. Say 10 or so. So just toss the commands in script with & at the end of the line and/or grouped
(dd... ; dd... ;dd...)&
Or just paste a bunch in a window.

I'll include and attach here a perl script that is pretty close to your needs and which can run a selectable number of streams in parallel taking note of the stat time and results. For now it READS, to allow testing.
Once satisfied replace if with of and null with zero. No I did not write this just for you :-). I had something very similar handy.
Input param is a list of (raw) device names

hth,
Hein.

#!/bin/perl
$file = shift (@ARGV);
$max_streams = shift (@ARGV);

die "Must provide file" unless $file;
$max = ($max_streams)? int ($max_streams) : 10;

open (FILE, $file) || die "Error open $file";
while () {
if ($par++ >= $max) {
$pid = wait();
$par--;
$s = 1;
$s++ while (($stream[$s] != $pid) && ($s <= $max) );
die "Lost child process ?" if ($s > $max);
} else {
$s = $par;
}
$pid = fork();
if ($pid) {
$stream[$s] = $pid;
} else {
($sec,$min,$hour) = localtime(time);
$date = sprintf("%02d:%02d:%02d ",$hour,$min,$sec);
open (LOG, ">>${file}_${s}.log" );
print LOG $date, $_;
close(LOG);
chop ($_);
exec ("dd of=/dev/null bs=128k count=100 if=$_ 2>> ${file}_${s}.log ")
}
}
close (FILE);

wait() while (--$par > 0);

Re: using dd command to zero out disks

RolandH — Mon, 08 Mar 2004 08:11:24 GMT

Have you ever heard about the command "mediainit". This is the best way to erase data on you disk.

Regards
Roland