From owner-freebsd-questions Sat Jul 8 11:46:26 2000 Delivered-To: freebsd-questions@freebsd.org Received: from implode.root.com (root.com [209.102.106.178]) by hub.freebsd.org (Postfix) with ESMTP id E2C6A37B8C1 for ; Sat, 8 Jul 2000 11:46:23 -0700 (PDT) (envelope-from dg@implode.root.com) Received: from implode.root.com (localhost [127.0.0.1]) by implode.root.com (8.8.8/8.8.5) with ESMTP id LAA27681; Sat, 8 Jul 2000 11:35:03 -0700 (PDT) Message-Id: <200007081835.LAA27681@implode.root.com> To: Emmanuel Gravel Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Performance issues with dd In-reply-to: Your message of "Fri, 07 Jul 2000 19:59:40 PDT." <3966991C.7BB8086A@earthlink.net> From: David Greenman Reply-To: dg@root.com Date: Sat, 08 Jul 2000 11:35:03 -0700 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG >As a backup measure, I'm using two hard drives of the same size, >but only mounting one, and I have a cron job that dd's one to >the other every night. The drives are 18 GB U160 SCSI, on a >AHA-29160N. The whole process takes 45 minutes. A quick calc >tells me it should be finished at best in 2 minutes, at peak >rate. This is over a 20x difference. > >Does anyone have any idea why it's taking so long? Is it just >dd that's the problem? The CPU is a PIII 650, and there's more >than enough memory to go, so I don't think the CPU would be >any kind of an impact here. Is there a better app out there >to do the job? I'm dumping one full raw device to the other, >not individual partitions. Could that be another problem? > >Thanks for any input, I'm at a complete loss here. You'll probably want to have "bs=64k" for best performance, but if that doesn't speed it up enough, then the slowness is likely due to the target drive not doing write buffering (write cache disable is 1 in mode page 8). This will cause it to do one write per revolution. -DG David Greenman Co-founder, The FreeBSD Project - http://www.freebsd.org Manufacturer of high-performance Internet servers - http://www.terasolutions.com Pave the road of life with opportunities. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message