From owner-freebsd-stable@FreeBSD.ORG Wed Nov 19 14:21:01 2014 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id B44FB442 for ; Wed, 19 Nov 2014 14:21:01 +0000 (UTC) Received: from kagate.punkt.de (kagate.punkt.de [217.29.33.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4B8C2D90 for ; Wed, 19 Nov 2014 14:21:00 +0000 (UTC) Received: from hugo10.ka.punkt.de ([217.29.45.10]) by gate1.intern.punkt.de with ESMTP id sAJE7h34068851 for ; Wed, 19 Nov 2014 15:07:43 +0100 (CET) Received: from hausen-mbp-5.intern.punkt.de (hausen-mbp-5.intern.punkt.de [217.29.45.148]) by hugo10.ka.punkt.de (8.14.2/8.14.2) with ESMTP id sAJE7hnd076919 for ; Wed, 19 Nov 2014 15:07:43 +0100 (CET) (envelope-from hausen@punkt.de) From: "Patrick M. Hausen" Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: 10.1 fresh install and 4k alignment Message-Id: Date: Wed, 19 Nov 2014 15:07:43 +0100 To: "freebsd-stable@freebsd.org List" Mime-Version: 1.0 (Mac OS X Mail 8.1 \(1993\)) X-Mailer: Apple Mail (2.1993) X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Nov 2014 14:21:01 -0000 Hi, all, I just installed a new machine with 10.1-RELEASE using the memstick = installer and chosing ZFS mirror root as the disk layout. I did check the "4k" option, watched the installer do the necessary gnop = dance and the pool seems to be OK: root@seleniumhub:~ # zdb | grep ashift ashift: 12 But this puzzles me a bit: root@seleniumhub:~ # gpart list ada0 Mediasize: 524288 (512K) Sectorsize: 512 ... Providers: 1. Name: ada0p1 Mediasize: 524288 (512K) Sectorsize: 512 ... end: 1057 start: 34 ... 3. Name: ada0p3 Mediasize: 465747565056 (434G) Sectorsize: 512 ... type: freebsd-zfs ... end: 976773134 start: 67109922 None of the start sector numbers is a multiple of 8, neither are the end = sectors a multiple of 8 minus 1. So the pool uses a 4k block size but it starts on an odd multiple of 2k = on the platter - do I see this correctly? Isn't it absolutely necessary that the simulated 4k blocks are laid out = so that the first is made from 512 byte sectors 0-7, the second from 8-15 and so on? Then why does the installer start the first partition at 512 byte sector = 34? While I'm at it, this magic number is everywhere in the older documentation, e.g. for = manually installing FreeBSD 8 with gptzfsboot - where does that 34 come from? = It's not a power of 2 nor is it one of the historical CHS magic numbers that = would mean a cylinder boundary or similar. Size of the GPT partition table itself? Is this a bug in the installer? Will I still have to layout the disks = manually if I want 4k alignment? What's a good offset for the first partition in this case? = Anything bigger than 34 that's a multiple of 8 - 40 or 64? Thanks in advance Patrick --=20 punkt.de GmbH * Kaiserallee 13a * 76133 Karlsruhe Tel. 0721 9109 0 * Fax 0721 9109 100 info@punkt.de http://www.punkt.de Gf: J=C3=BCrgen Egeling AG Mannheim 108285