From owner-freebsd-fs@FreeBSD.ORG  Sun Mar 10 23:59:18 2013
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@freebsd.org
Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115])
 by hub.freebsd.org (Postfix) with ESMTP id E40C3D6E
 for <freebsd-fs@freebsd.org>; Sun, 10 Mar 2013 23:59:18 +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 9B306827
 for <freebsd-fs@freebsd.org>; Sun, 10 Mar 2013 23:59:18 +0000 (UTC)
Received: from wonkity.com (localhost [127.0.0.1])
 by wonkity.com (8.14.6/8.14.6) with ESMTP id r2ANxHxN009350;
 Sun, 10 Mar 2013 17:59:17 -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 r2ANxHob009347;
 Sun, 10 Mar 2013 17:59:17 -0600 (MDT)
 (envelope-from wblock@wonkity.com)
Date: Sun, 10 Mar 2013 17:59:17 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: Adam Nowacki <nowakpl@platinum.linux.pl>
Subject: Re: Aligning MBR for ZFS boot help
In-Reply-To: <513D0E90.5090105@platinum.linux.pl>
Message-ID: <alpine.BSF.2.00.1303101749370.8481@wonkity.com>
References: <513C1629.50501@caltel.com> <513D0E90.5090105@platinum.linux.pl>
User-Agent: Alpine 2.00 (BSF 1167 2008-08-23)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7
 (wonkity.com [127.0.0.1]); Sun, 10 Mar 2013 17:59:17 -0600 (MDT)
Cc: freebsd-fs@freebsd.org
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 10 Mar 2013 23:59:19 -0000

On Sun, 10 Mar 2013, Adam Nowacki wrote:

> I don't think zfsboot is aware of BSD disklabel (offsets other than 0 won't 
> boot). Is there any reason you are using BSD disklabel and not two partition 
> MBR?

MBR slices created on FreeBSD are forced to CHS alignment, pretty much 
always misaligned for 4K-block hard drives or SSDs.

> I also don't think there is any merit in aligning to 1MiB. Most ZFS IOs will 
> be aligned to sector size (ashift). Unless ZFS pool is created with higher 
> ashift then the 63 sector offset is as good as any.

If the drive has 4K sectors, that will be misaligned, potentially 
cutting speeds drastically even if ashift is 9.