From owner-freebsd-stable Tue Apr 2 05:26:58 1996 Return-Path: owner-stable Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id FAA22055 for stable-outgoing; Tue, 2 Apr 1996 05:26:58 -0800 (PST) Received: from mail.telstra.com.au (mail.telstra.com.au [192.148.160.10]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id FAA22045 for ; Tue, 2 Apr 1996 05:26:53 -0800 (PST) Received: from mail_gw.fwall.telecom.com.au(192.148.147.10) by mail via smap (V1.3) id sma016094; Tue Apr 2 16:32:17 1996 Received: from netbsd08.dn.itg.telecom.com.au(144.139.63.32) by mail_gw.telecom.com.au via smap (V1.3) id sma014684; Tue Apr 2 23:21:18 1996 Received: from netbsd08.dn.itg.telecom.com.au (netbsd08.dn.itg.telecom.com.au [144.139.63.32]) by netbsd08.dn.itg.telecom.com.au (8.6.8/8.6.6) with SMTP id VAA00732; Tue, 2 Apr 1996 21:33:35 +0800 Date: Tue, 2 Apr 1996 21:33:34 +0800 (WST) From: Terry Dwyer To: Michael Smith cc: Zeki Basbuyuk , stable@FreeBSD.org Subject: Re: SCSI Performance under -stable/-current In-Reply-To: <199604021022.TAA14221@genesis.atrad.adelaide.edu.au> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-stable@FreeBSD.org X-Loop: FreeBSD.org Precedence: bulk On Tue, 2 Apr 1996, Michael Smith wrote: > Zeki Basbuyuk stands accused of saying: > > > How do you get this speed? I thought there is a physical limitation > > on how much speed you can get for a hard drive. The calculation is > > as follows. 120 rps (revs per sec assuming 7200 rpm drive) X 40 > > sectors per track (average or above average) X 512 bps (bytes per > > sector) = 2.4 MB /sec. To get 6 MB either spt needs to increase to > > 100 or so or rotation needs to be increased. > > One should always temper theory with reality. You can go a lot faster by > striping your sectors across several surfaces, for example. For example, multiply the above figure by the number of physical heads on the drive, 5 for a barracuda. It looks like he's only calculated for one head. I also seem to remember reading somewhere that the _internal_ data transfer rate was about 47 to 70Mb/sec., at least for a barracuda. > > Reality shows us that the more agressive drives will happily outrun the > sustained rate your envelope calculation suggests, so I guess reality is > more complicated that you're allowing for 8) > > > Tom > > -- > ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[ > ]] Genesis Software genesis@atrad.adelaide.edu.au [[ > ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ > ]] realtime instrument control (ph/fax) +61-8-267-3039 [[ > ]] Collector of old Unix hardware. "Where are your PEZ?" The Tick [[ > _-_|\ Terry Dwyer E-Mail: tdwyer@netbsd08.dn.itg.telecom.com.au / \ System Administrator Phone: +61 9 491 5161 Fax: +61 9 221 2631 *_.^\_/ Telecom Australia Telstra Corporation MIME capable mailer v Perth WA ( I do not speak for Telstra or Telecom )