From owner-freebsd-hackers Wed Nov 11 04:01:46 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id EAA07994 for freebsd-hackers-outgoing; Wed, 11 Nov 1998 04:01:46 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from server.noc.demon.net (server.noc.demon.net [193.195.224.4]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id EAA07988 for ; Wed, 11 Nov 1998 04:01:44 -0800 (PST) (envelope-from fanf@demon.net) Received: by server.noc.demon.net; id MAA26717; Wed, 11 Nov 1998 12:01:25 GMT Received: from fanf.noc.demon.net(195.11.55.83) by inside.noc.demon.net via smap (3.2) id xma026685; Wed, 11 Nov 98 12:01:10 GMT Received: from fanf by fanf.noc.demon.net with local (Exim 1.73 #2) id 0zdZBf-0003dj-00; Wed, 11 Nov 1998 12:15:51 +0000 To: hackers@FreeBSD.ORG From: Tony Finch Subject: Re: SCSI vs. DMA33.. Newsgroups: chiark.mail.freebsd.hackers In-Reply-To: <19981111162000.O20374@freebie.lemis.com> Organization: Deliberate Obfuscation To Amuse Tony References: <98Nov11.134648jst.21907@ns.isi.co.jp> <98Nov11.134648jst.21907@ns.isi.co.jp> Message-Id: Date: Wed, 11 Nov 1998 12:15:51 +0000 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Greg Lehey wrote: > [...] >They say, though, that SCSI drives work better with multiple requests >outstanding... > >$ dd if=/dev/rsd0c bs=32k count=1000 of=/dev/null & dd if=/dev/rsd1c bs=32k count=1000 of=/dev/null [...] >I must say, I'm surprised. This makes it look like there's more of a >performance hit with concurrent requests on SCSI than on IDE. [...] Our canonical examples of applications that benefit from SCSI is a web server or proxy cache, because they tend to exercise the disks' ability to do random seeks. Given that disks frequently lie through their teeth about their geometry and do things like transparent bad block remapping, letting the disk do its own request scheduling is probably a Good Thing. Obviously you have to have a controller that can queue up a decent number of outstanding requests so care is required when looking at the specs... Sorry, I don't have performance numbers to hand right now. Tony. -- gg yhf**f.a.n.finch dot@dotat.at fanf@demon.net To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message