Subject: Re: Strange system behaviour when copying disks
From: Olaf =?iso-8859-2?Q?Fr=B1czyk?= <olaf@cbk.poznan.pl>
To: linux-xfs@oss.sgi.com
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Date: 16 May 2003 10:29:43 +0200
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On Fri, 2003-05-16 at 08:25, Ethan Benson wrote:
> 
> what happens if you use bs=4096 to dd ? 
> 
> doing a strace of cat shows it appears to do read/writes in 4096 byte
> blocks perhaps this is making a difference.
I have tried 512,1024,2048,4096,8192,16384.
It works smoothly with all above values.
The only difference was with 512: the speed was cut about half.
dd if=/dev/zero of=/dev/hda1 bs=1 count=100000000 also doesn't make the
system unresponsive

So, it is not because of block size.
Also cat /dev/hda1 > /dev/null doesn't hurt.

But cat /dev/zero > /dev/hda1 makes the system even more unresponsive
than doing cat /dev/hda1 > /dev/hdc1

So the output redirection from bash does something strange for normal
block devices. I think.

Does someone has an idea what is the cause?

Regards,

Olaf