Date: Sat, 08 Jul 2000 11:35:03 -0700 From: David Greenman <dg@root.com> To: Emmanuel Gravel <egravel@earthlink.net> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Performance issues with dd Message-ID: <200007081835.LAA27681@implode.root.com> In-Reply-To: Your message of "Fri, 07 Jul 2000 19:59:40 PDT." <3966991C.7BB8086A@earthlink.net>
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>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
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