From owner-freebsd-doc@FreeBSD.ORG Sun Jun 10 14:35:40 2012 Return-Path: Delivered-To: doc@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id DDA8D106564A for ; Sun, 10 Jun 2012 14:35:39 +0000 (UTC) (envelope-from hrs@FreeBSD.org) Received: from mail.allbsd.org (gatekeeper.allbsd.org [IPv6:2001:2f0:104:e001::32]) by mx1.freebsd.org (Postfix) with ESMTP id DEB508FC15 for ; Sun, 10 Jun 2012 14:35:38 +0000 (UTC) Received: from alph.allbsd.org (p4242-ipbf1504funabasi.chiba.ocn.ne.jp [118.7.211.242]) (authenticated bits=128) by mail.allbsd.org (8.14.5/8.14.5) with ESMTP id q5AEZIdN047290; Sun, 10 Jun 2012 23:35:28 +0900 (JST) (envelope-from hrs@FreeBSD.org) Received: from localhost (localhost [IPv6:::1]) (authenticated bits=0) by alph.allbsd.org (8.14.4/8.14.4) with ESMTP id q5AEZFFf090966; Sun, 10 Jun 2012 23:35:17 +0900 (JST) (envelope-from hrs@FreeBSD.org) Date: Sun, 10 Jun 2012 23:15:55 +0900 (JST) Message-Id: <20120610.231555.975873460722378457.hrs@allbsd.org> To: wblock@wonkity.com From: Hiroki Sato In-Reply-To: References: <20120606.185023.497714372668376681.hrs@allbsd.org> X-PGPkey-fingerprint: BDB3 443F A5DD B3D0 A530 FFD7 4F2C D3D8 2793 CF2D X-Mailer: Mew version 6.4.50 on Emacs 23.4 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Multipart/Signed; protocol="application/pgp-signature"; micalg=pgp-sha1; boundary="--Security_Multipart(Sun_Jun_10_23_15_55_2012_960)--" Content-Transfer-Encoding: 7bit X-Virus-Scanned: clamav-milter 0.97.4 at gatekeeper.allbsd.org X-Virus-Status: Clean X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (mail.allbsd.org [133.31.130.32]); Sun, 10 Jun 2012 23:35:28 +0900 (JST) X-Spam-Status: No, score=-98.6 required=13.0 tests=CONTENT_TYPE_PRESENT, QENCPTR1,RCVD_IN_RP_RNBL,USER_IN_WHITELIST autolearn=no version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on gatekeeper.allbsd.org Cc: doc@FreeBSD.org Subject: Re: Handbook mirroring section X-BeenThere: freebsd-doc@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Documentation project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 10 Jun 2012 14:35:40 -0000 ----Security_Multipart(Sun_Jun_10_23_15_55_2012_960)-- Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Warren Block wrote in : wb> On Wed, 6 Jun 2012, Hiroki Sato wrote: wb> > BTW, do you (or anyone) know the common failure pattern when trying wb> > to use GPT + gmirror of the whole disk? IIRC it was a metadata wb> > corruption but I do not remember when it happens. wb> wb> When gmirror is used to mirror two disks, metadata goes in the last wb> block of each. If GPT partitioning is used on the mirror, the GPT wb> secondary partition table overwrites the mirror metadata because, by wb> specification, GPT puts that secondary table at the end of the wb> physical drive, rather than inside the gmirror logical device. I think the interpretation that "GPT specification says the backup header must be at the last LBA of the *physical* disk" is just making things too harder. The problem is that BIOS and the loader does not support a gmirror logical volume, and the incompletely-configured volume is recognized for a short time during a boot due to it. The location of the backup header is recorded in the Backup LBA field in the primary header, so everything will work fine as long as the pre-boot programs support it and the primary header is not corrupted. I do not think this situation is against standards conformance though it is suboptimal. If we can teach GEOM to BIOS and/or UEFI it would be the best, but it is not likely. What I want to know is whether there are some practical difficulties when we apply the whole-disk mirroring procedure for MBR to a GPT-based system. Overwrite of the last LBA should not happen if FreeBSD is the only one system on the disk. One common failure scenario is when the primary header is corrupted. If there are more, I want to know it. -- Hiroki ----Security_Multipart(Sun_Jun_10_23_15_55_2012_960)-- Content-Type: application/pgp-signature Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEABECAAYFAk/UrBsACgkQTyzT2CeTzy0e8ACeK1a79nR2lzkvI7sXSi9xti/H ku8Anjs0vxvWjjzSuDPwP+xvJ5N2JInL =595C -----END PGP SIGNATURE----- ----Security_Multipart(Sun_Jun_10_23_15_55_2012_960)----