From owner-freebsd-fs@FreeBSD.ORG Mon Mar 11 00:39:33 2013 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 083632B1 for ; Mon, 11 Mar 2013 00:39:33 +0000 (UTC) (envelope-from wblock@wonkity.com) Received: from wonkity.com (wonkity.com [67.158.26.137]) by mx1.freebsd.org (Postfix) with ESMTP id AFC05974 for ; Mon, 11 Mar 2013 00:39:32 +0000 (UTC) Received: from wonkity.com (localhost [127.0.0.1]) by wonkity.com (8.14.6/8.14.6) with ESMTP id r2B0dU2X009599; Sun, 10 Mar 2013 18:39:30 -0600 (MDT) (envelope-from wblock@wonkity.com) Received: from localhost (wblock@localhost) by wonkity.com (8.14.6/8.14.6/Submit) with ESMTP id r2B0dUKW009596; Sun, 10 Mar 2013 18:39:30 -0600 (MDT) (envelope-from wblock@wonkity.com) Date: Sun, 10 Mar 2013 18:39:30 -0600 (MDT) From: Warren Block To: Dennis Glatting Subject: Re: Aligning MBR for ZFS boot help In-Reply-To: <1362951595.99445.2.camel@btw.pki2.com> Message-ID: References: <513C1629.50501@caltel.com> <513CD9AB.5080903@caltel.com> <513CE369.4030303@caltel.com> <1362951595.99445.2.camel@btw.pki2.com> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (wonkity.com [127.0.0.1]); Sun, 10 Mar 2013 18:39:30 -0600 (MDT) Cc: freebsd-fs@freebsd.org X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 Mar 2013 00:39:33 -0000 On Sun, 10 Mar 2013, Dennis Glatting wrote: > Sorry for the stupid question but is this issue (and issues) and > procedures written up somewhere? The wiki shows using GPT: https://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/9.0-RELEASE The issue with MBR is that FreeBSD strictly follows the standard of alignment to CHS values. However, for the last couple of decades, drives have used variable geometry to fit more data on the outside tracks, so CHS values don't apply any more. Combine this with the new need to align MBR slices to particular values of 4K or 1M, and FreeBSD has a problem. Solution: use GPT when possible. But some systems won't boot from GPT. If MBR partitioning is required, and alignment is needed, use some other operating system to create the MBR, and don't try to edit the slices on FreeBSD. I don't know if anyone has documented all this in one place. If FreeBSD had a way to turn off the strict enforcement of CHS values for MBR, it would make that unnecessary.