From owner-freebsd-questions Sun Sep 1 16: 0:34 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 00BE037B400 for ; Sun, 1 Sep 2002 16:00:29 -0700 (PDT) Received: from smtp.infracaninophile.co.uk (happy-idiot-talk.infracaninophile.co.uk [81.2.69.218]) by mx1.FreeBSD.org (Postfix) with ESMTP id 8D04643E6A for ; Sun, 1 Sep 2002 16:00:27 -0700 (PDT) (envelope-from m.seaman@infracaninophile.co.uk) Received: from happy-idiot-talk.infracaninophile.co.uk ([IPv6:::1]) by smtp.infracaninophile.co.uk (8.12.5/8.12.5) with ESMTP id g81N0QGk013212; Mon, 2 Sep 2002 00:00:26 +0100 (BST) (envelope-from matthew@happy-idiot-talk.infracaninophile.co.uk) Received: (from matthew@localhost) by happy-idiot-talk.infracaninophile.co.uk (8.12.5/8.12.5/Submit) id g81N0LR9013211; Mon, 2 Sep 2002 00:00:21 +0100 (BST) Date: Mon, 2 Sep 2002 00:00:21 +0100 From: Matthew Seaman To: Warren Block Cc: Matthew Seaman , FreeBSD LIST Subject: Re: dd if=/dev/zero of=/dev/ad1 Message-ID: <20020901230021.GC12421@happy-idiot-talk.infracaninophi> References: <20020901223639.GA12421@happy-idiot-talk.infracaninophi> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.1i Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG 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 0 42 64.00 556 34.74 0 0 2 3 95 0 43 64.00 557 34.82 0 0 1 3 96 Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks Savill Way Marlow Tel: +44 1628 476614 Bucks., SL7 1TH UK To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message