Date: Thu, 12 Jan 2006 09:39:23 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Christoph Kukulies <kuku@www.kukulies.org> Cc: freebsd-hackers@freebsd.org Subject: Re: increasing dd disk to disk transfer rate Message-ID: <20060112153919.GA21009@dan.emsphone.com> In-Reply-To: <200601120948.k0C9mcqR092895@www.kukulies.org> References: <200601120948.k0C9mcqR092895@www.kukulies.org>
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In the last episode (Jan 12), Christoph Kukulies said: > My notebooks' hard disk, a Hitachi Travelstar 80 GB starts to develop > read errors. I have FreeBSD and Win XP on that disk. Although FreeBSD > ist still working , the errors in the Windows partition are causing > Windows do ask for a filesystem check nearly everytime I reboot the > computer. One time the error was in the hibernate.sys file, which > impedes powering up quickly after a hibernate. > > Anyway, I decided to buy a second identical hard disk and tried to > block by block copy the old disk to the new one using > > dd if=/dev/ad2 of=/dev/ad3 conv=noerror > > The process is running now since yesterday evening and it is at 53 MB > at a transfer rate of about 1.1 MB/s. Everybody has mentioned the first obvious fix: raise your blocksize from the default 512 bytes. The second fix addresses the problem that with a single dd, you are either reading or writing. If you pipe the first dd into a second one, it'll let you run at the max speed of the slowest device. dd if=/dev/ad2 conv=noerror,sync bs=64k | dd of=/dev/ad3 bs=64k -- Dan Nelson dnelson@allantgroup.com
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