[ale] Understanding dd and/or /dev/zero

[Greg Freemyer]

On Mon, 10 Jan 2005 19:15:23 -0500, Danny Cox <danscox at mindspring.com> wrote:
> Greg,
> 
> On Mon, 2005-01-10 at 16:54 -0500, Greg Freemyer wrote:
> > I've noticed that I get a log of disk read activitity on /dev/hdc when I do
> >
> >     dd if=/dev/zero of=/dev/hdc
> >
> > I'm using "iostat -d 5" to see the read activity, and it is really
> > slowing down the above.
> >
> > I have no idea why there is disk read activity, and the machine is
> > doing nothing else.  Also if I kill the above dd, the read activity
> > stops.
> 
>         I don't know why you're seeing reads either, unless iostat is wrong, or
> the kernel is.
> 
>         As another data point, try bumping up the block size of the dd like
> this:
> 
>         dd bs=1024M if=/dev/zero of=/dev/hdc
> 
> and stand well back ;-).
> 
> --
> kernel, n.: A part of an operating system that preserves the
> medieval traditions of sorcery and black art.
> 
> Danny
> 
>
Danny,

I'll do it tomorrow, but I assume you are trying to cause swapping???

i.e.  I only have 512 MB in my test machine.

Greg