From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1UGXRn-0003Kp-FI for mharc-grub-devel@gnu.org; Fri, 15 Mar 2013 12:25:35 -0400 Received: from eggs.gnu.org ([208.118.235.92]:33742) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UGXRk-0003Ea-WE for grub-devel@gnu.org; Fri, 15 Mar 2013 12:25:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UGXRg-0002QC-My for grub-devel@gnu.org; Fri, 15 Mar 2013 12:25:32 -0400 Received: from mail-qa0-f44.google.com ([209.85.216.44]:58723) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UGXRg-0002Q0-HS for grub-devel@gnu.org; Fri, 15 Mar 2013 12:25:28 -0400 Received: by mail-qa0-f44.google.com with SMTP id bv4so406039qab.10 for ; Fri, 15 Mar 2013 09:25:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:message-id:date:from:user-agent:mime-version:to:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=n75ZogPx1aLQ/FLcl1QA39JuGa83JKMJHKHNAlINV5A=; b=sfiecOSJVEmVxOPLTSPActPdnxLVDwDLq2qlVgMW6KFneluaD258+X1WLb9MWtgGhe c+bOU2i/ztQIx6wfnTz6Fl/8wi4FUZOCAE61OD0SF+hgoK5fQ8+FdKFEmYYioJNCCPEt NAQuljLE7oGkcFuNmkKWq1cwR+JsVXNhGd3SNyVP3nnJeGNZi6yelcAwItptYlv2yolR 4eXak6P1UETboj0Js72sU4BYZk4raWhP+pCalEunpgTjhX9sttaV3mBH2KnLJC5DWHkG CXZgHA9+ekRmsPGGy+8YKbvhhTTCjgiwChqxY1Sb/8xPC4r96hwrlIjbIgSg2Fksy0xZ RDwg== X-Received: by 10.224.61.72 with SMTP id s8mr389651qah.12.1363364726403; Fri, 15 Mar 2013 09:25:26 -0700 (PDT) Received: from [192.168.0.75] (cpe-70-123-218-92.satx.res.rr.com. [70.123.218.92]) by mx.google.com with ESMTPS id ku2sm4103446qeb.4.2013.03.15.09.25.24 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 15 Mar 2013 09:25:25 -0700 (PDT) Message-ID: <51434B73.6000804@gmail.com> Date: Fri, 15 Mar 2013 11:25:23 -0500 From: Bruce Dubbs User-Agent: Mozilla/5.0 (X11; Linux i686; rv:13.0) Gecko/20120628 Firefox/13.0.1 SeaMonkey/2.10.1 MIME-Version: 1.0 To: The development of GNU GRUB Subject: Re: USB3 3TB HDD boot References: <1360696755.21718.53.camel@pracovna> <20130304191935.GF20462@csclub.uwaterloo.ca> <5134F71F.1040300@gmail.com> <20130304194307.GJ20462@csclub.uwaterloo.ca> <51359D36.1040105@gmail.com> <4C3F5BBE-86BD-488F-A5FE-9D834B428189@colorremedies.com> <20130315063812.4b84a40f@opensuse.site> <20130315145129.GA1271@csclub.uwaterloo.ca> <318BCF38-E9A6-4AE3-907B-21F22CC00A4B@colorremedies.com> In-Reply-To: <318BCF38-E9A6-4AE3-907B-21F22CC00A4B@colorremedies.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 209.85.216.44 X-BeenThere: grub-devel@gnu.org X-Mailman-Version: 2.1.14 Precedence: list Reply-To: The development of GNU GRUB List-Id: The development of GNU GRUB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Mar 2013 16:25:35 -0000 Chris Murphy wrote: > > On Mar 15, 2013, at 8:51 AM, Lennart Sorensen > wrote: > >> On Thu, Mar 14, 2013 at 08:56:18PM -0600, Chris Murphy wrote: >>> Right, for a 4Kn drive, to read LBA 1 and get the GPT header I'd >>> need: >>> >>> sudo dd if=/dev/disk3 skip=8 count=1 2>/dev/null | hexdump -C >> >> Wouldn't using 'bs=4096' make things simpler and more obvious? > > How would it? > > These structures are still predicated on a 512 byte block. The MBR is > always 512 bytes, but on a 4096/4096 4Kn drive, LBA 0 is 4096 bytes. > So if I don't want to see 3584 bytes of useless garbage, I can't set > the dd block size to 4096, or I get extra information. > > If I want to see just the GPT header, which while only ~92 bytes, by > spec it gets its own sector, there's far less superfluous information > using a bs of 512 bytes than 4096 bytes. There is more than one way to do things. sudo dd if=/dev/disk3 bs=4096 skip=1 count=1 | cut -c 1-92 | hexdump -C is one way that matches the physical drive. The first mentioned way works too, but doesn't reflect as well what is really going on. -- Bruce