From owner-freebsd-questions  Sun Sep  1 16:38:58 2002
Delivered-To: freebsd-questions@freebsd.org
Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id EB0BC37B400
	for <FreeBSD-Questions@FreeBSD.ORG>; Sun,  1 Sep 2002 16:38:54 -0700 (PDT)
Received: from wonkity.com (wonkity.com [63.93.4.4])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 1E83643E6A
	for <FreeBSD-Questions@FreeBSD.ORG>; Sun,  1 Sep 2002 16:38:54 -0700 (PDT)
	(envelope-from wblock@wonkity.com)
Received: from wonkity.com (localhost.wonkity.com [127.0.0.1])
	by wonkity.com (8.12.1/8.11.6) with ESMTP id g81NcquF013407;
	Sun, 1 Sep 2002 17:38:53 -0600 (MDT)
	(envelope-from wblock@wonkity.com)
Received: from localhost (wblock@localhost)
	by wonkity.com (8.12.1/8.12.1/Submit) with ESMTP id g81NcpSn013404;
	Sun, 1 Sep 2002 17:38:51 -0600 (MDT)?g
	(envelope-from wblock@wonkity.com)
Date: Sun, 1 Sep 2002 17:38:51 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: Matthew Seaman <m.seaman@infracaninophile.co.uk>
Cc: FreeBSD LIST <FreeBSD-Questions@FreeBSD.ORG>
Subject: Re: dd if=/dev/zero of=/dev/ad1
In-Reply-To: <20020901230021.GC12421@happy-idiot-talk.infracaninophi>
Message-ID: <Pine.BSF.4.21.0209011736520.13398-100000@wonkity.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: owner-freebsd-questions@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-questions.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-questions>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-questions>
X-Loop: FreeBSD.ORG

On Mon, 2 Sep 2002, Matthew Seaman wrote:

> On Sun, Sep 01, 2002 at 04:52:39PM -0600, Warren Block wrote:
> > On Sun, 1 Sep 2002, Matthew Seaman wrote:
> > 
> > > It's part of the IDE specification: 128k is the maximum IO transfer
> > > size.  Oh --- the equivalent figure for SCSI discs is 64kB.
> > 
> > I'm reasonably certain that for SCSI it's 64K *blocks* of 512 bytes
> > each, or 32M.  Some systems may have driver limitations that break
> > transfers up into 64K chunks, though.
> 
> Like FreeBSD perhaps?
> 
>     happy-idiot-talk:/home/matthew:# dd if=/dev/da0c of=/dev/null bs=1m &
>     [2] 13192
>     happy-idiot-talk:/home/matthew:# iostat da0 1
>           tty             da0             cpu
>      tin tout  KB/t tps  MB/s  us ni sy in id
>        5   11  0.00   0  0.00   2  0  0  3 94
>        1   43 64.00 556 34.77   1  0  2  2 95
>        0   43 64.00 557 34.84   1  0  0  4 95

Sure.  The point being that with IDE, 128Kbyte transfers are a result of
the hardware.  With SCSI, 64Kbyte transfers are the result of the
driver, not the hardware.

-Warren Block * Rapid City, South Dakota USA


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message