From owner-freebsd-questions@FreeBSD.ORG Sun May 23 23:23:10 2010 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id A5858106564A for ; Sun, 23 May 2010 23:23:10 +0000 (UTC) (envelope-from bc979@lafn.org) Received: from zoom.lafn.org (zoom.lafn.ORG [206.117.18.8]) by mx1.freebsd.org (Postfix) with ESMTP id 822D58FC13 for ; Sun, 23 May 2010 23:23:10 +0000 (UTC) Received: from [10.0.1.4] (pool-71-109-144-133.lsanca.dsl-w.verizon.net [71.109.144.133]) (authenticated bits=0) by zoom.lafn.org (8.14.3/8.14.2) with ESMTP id o4NNN84Z034509 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NO); Sun, 23 May 2010 16:23:09 -0700 (PDT) (envelope-from bc979@lafn.org) References: <76E02DE6-9A61-4D24-9638-ABB7418711D9@lafn.org> <4BF9ACDE.6050502@otenet.gr> In-Reply-To: <4BF9ACDE.6050502@otenet.gr> Mime-Version: 1.0 (Apple Message framework v1078) Content-Type: text/plain; charset=utf-8 Message-Id: Content-Transfer-Encoding: quoted-printable From: Doug Hardie Date: Sun, 23 May 2010 16:23:08 -0700 To: Manolis Kiagias X-Mailer: Apple Mail (2.1078) X-Virus-Scanned: clamav-milter 0.95.3 at zoom.lafn.org X-Virus-Status: Clean Cc: freebsd-questions - Subject: Re: Verifying a DVD X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 23 May 2010 23:23:10 -0000 On 23 May 2010, at 15:31, Manolis Kiagias wrote: > On 24/05/2010 1:23 =CF=80.=CE=BC., Doug Hardie wrote: >> I am periodically backing up a bunch of files to DVD. I use mkisofs = to create the original image and growisofs to write it to a real DVD. = However, at that point I want to verify that the write was successful. = I tried using dd to read back in the DVD to a file. Its interesting = that the bs parameter must be at least 2048 or dd complains about a = parameter error. However, the big issues is that the original image = file is shorter than the read file. The difference is 10240 bytes. = This difference is the same for bs 2048, 10240, or 102400. It appears = that dd is adding one last block. Is there a way to prevent this or = remove that block? >>=20 >=20 > Use the count=3D parameter in dd to read the exact count of blocks in = the > DVD. Use isoinfo to obtain this information from the media itself. = Have > a look at the instructions here: >=20 > http://www.troubleshooters.com/linux/coasterless.htm >=20 >=20 Thanks. That works great. I did discover that appending 10240 zeros to = the end of the original iso file also works. However, I am not = convinced that it will always be that value. The approach above should = be more reliable.=