From owner-freebsd-questions Wed Aug 7 8:28: 2 2002 Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1278337B400 for ; Wed, 7 Aug 2002 08:27:59 -0700 (PDT) Received: from sage-one.net (adsl-65-71-135-137.dsl.crchtx.swbell.net [65.71.135.137]) by mx1.FreeBSD.org (Postfix) with ESMTP id 0253C43E5E for ; Wed, 7 Aug 2002 08:27:58 -0700 (PDT) (envelope-from jackstone@sage-one.net) Received: from sagea (sagea [192.168.0.3]) by sage-one.net (8.11.6/8.11.6) with SMTP id g77FRpB14688; Wed, 7 Aug 2002 10:27:51 -0500 (CDT) (envelope-from jackstone@sage-one.net) Message-Id: <3.0.5.32.20020807102750.02d62db8@mail.sage-one.net> X-Sender: jackstone@mail.sage-one.net X-Mailer: QUALCOMM Windows Eudora Pro Version 3.0.5 (32) Date: Wed, 07 Aug 2002 10:27:50 -0500 To: "Siegbert Baude" , "Rob Ellis" From: "Jack L. Stone" Subject: Re: Best "bs" for dd copies (was: Re: Questions about vinum and failure of root partition) Cc: , =?Windows-1252?Q?S=F8ren_Schmidt?= In-Reply-To: <001c01c23e25$b05a1180$406a3c86@whwurm.uniulm.de> References: <005e01c23dcb$061acbb0$6602a8c0@swbell.net> <200208070101.g7711iU06306@clunix.cl.msu.edu> <005e01c23dcb$061acbb0$6602a8c0@swbell.net> <3.0.5.32.20020807085441.02d62db8@mail.sage-one.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG At 05:18 PM 8.7.2002 +0200, Siegbert Baude wrote: >Hi Jack, > >first an apology to Soeren for cc'ing him, but he probably is the best >man to answer this question (and a second one for not being able to >produce the correct letter for the spelling of his name *g*). > >Rob wrote: >> >then create a backup of the fbsd partitions on >> >the first disk, copying everything from ad0s1 to ad2s1: >> > >> > dd if=/dev/ad0s1 of=/dev/ad2s1 bs=102400 > >Jack wrote: >> My side question is about the "dd" command. Why did you choose the >> parameter "bs=102400" rather than any other?? I've been using 8192, >but >> have seen this switch all over the map, including 1024 to 1M. I know >it can >> make a difference in the time to do an image because of the sizing. >With >> 8192, I do an entire 40GB HD in 39 mins (1.4GHz CPU) but takes 49 mins >for >> a 1GHz CPU. > >I just experimented a bit last weekend, when I dd'ed a 80GB IBM >IC35L080AVVA07-0 to another disk of exactly the same type (needed a >bit-copy as backup, because the partition table was corrupted). > >I tried bs from standard 512 up to 8MB by always doubling the value from >try to try and found that 128k worked the best for me. That is quite >near to the proposed 100k of Rob. The transfer rate varied from 6 MB/s >to 20MB/s, if my memory works right. At least it was far away from the >33MB/s the UDMA-33 mode should give (the disks could do UDMA 100 and the >highpoint controller even UDMA 133, but I only had normal cables). IBM >claims its disk should transfer a sustained rate from 48MB/s to 23MB/s >depending on the zone. The disk cache is 2MB, btw. The board was an >Abit-BX133 with 256MB RAM and a PIII-850. > >So, if anybody knows how to calculate the best value out of the >technical parameters or can explain, why ~100k seems the best value (and >not e.g. something in the area of disk cache size) I also would be very >interested to hear. >What is the maximum at all, one can expect? Is it possible to reach the >maximum rate IBM claims for its disk with dd? > >Ciao >Siegbert > Thanks for the follow-up on the "dd bs" side question. Clearly this parameter makes a big difference as does the CPU speed, UDMA, etc. I too would like to know of any way to calculate, but probably what you did by trial is a good approach for each particular specific setup/environment. Best regards, Jack L. Stone, Administrator SageOne Net http://www.sage-one.net jackstone@sage-one.net To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message