Date: Mon, 30 Sep 2002 19:32:33 -0500 From: "Jack L. Stone" <jackstone@sage-one.net> To: Richard Tobin <richard@cogsci.ed.ac.uk>, "Pranav A. Desai" <pdesai1@cs.uh.edu>, <freebsd-questions@FreeBSD.ORG> Subject: Re: how to use 'dd' to create image of a hard drive? Message-ID: <3.0.5.32.20020930193233.028ece30@mail.sage-one.net> In-Reply-To: <200210010027.BAA18320@sorley.cogsci.ed.ac.uk> References: <Jack L. Stone's message of Mon, 30 Sep 2002 19:10:06 -0500>
next in thread | previous in thread | raw e-mail | index | archive | help
At 01:27 AM 10.1.2002 +0100, Richard Tobin wrote:
>> bs=102400 or bs=128k will dd faster though.... you can play with that.
>
>That's not my experience. 8k dd runs at disk speed (30-40 MB/s) on
>all the machines I've used recently when copying between different
>disks on different ATA controllers. Between disks on the same
>controller I only get about 13MB/s (why?) but there's no difference
>between 8k and 128k dd.
>
>-- Richard
>
Check your I/O. Try this:
dd if=/dev/ad0c of=/dev/null bs=128k &
and in the background do an 'iostat ad0 1'. Here's an example with an
IDE drive:
# iostat ad0 1
tty ad0 cpu
tin tout KB/t tps MB/s us ni sy in id
0 3 5.19 7 0.03 11 0 4 1 84
0 126 127.36 183 22.74 0 0 6 2 92
0 44 128.00 190 23.76 0 0 2 0 98
0 44 128.00 191 23.89 0 0 5 0 95
0 44 128.00 191 23.88 0 0 7 1 92
As you can see, it's really doing 128 kB transfers, for an average transfer
rate of almost 24 MB/s
Best regards,
Jack L. Stone,
Administrator
SageOne Net
http://www.sage-one.net
jackstone@sage-one.net
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3.0.5.32.20020930193233.028ece30>