From owner-freebsd-questions@FreeBSD.ORG Tue Dec 3 16:27:15 2013 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id CB378F08 for ; Tue, 3 Dec 2013 16:27:15 +0000 (UTC) Received: from wonkity.com (wonkity.com [67.158.26.137]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 633351FDD for ; Tue, 3 Dec 2013 16:27:15 +0000 (UTC) Received: from wonkity.com (localhost [127.0.0.1]) by wonkity.com (8.14.7/8.14.7) with ESMTP id rB3GRDvX023979; Tue, 3 Dec 2013 09:27:13 -0700 (MST) (envelope-from wblock@wonkity.com) Received: from localhost (wblock@localhost) by wonkity.com (8.14.7/8.14.7/Submit) with ESMTP id rB3GRCQi023976; Tue, 3 Dec 2013 09:27:13 -0700 (MST) (envelope-from wblock@wonkity.com) Date: Tue, 3 Dec 2013 09:27:12 -0700 (MST) From: Warren Block To: Julien Cigar Subject: Re: gmirror, gpart and MBR vs GPT in the Handbook In-Reply-To: <20131203092604.GA86280@mordor.lan> Message-ID: References: <201311301303210813.05DE187E@smtp.24cl.home> <201312011121580096.005D00FB@smtp.24cl.home> <20131202103122.GN66981@mordor.lan> <20131203092604.GA86280@mordor.lan> 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-4.4.3 (wonkity.com [127.0.0.1]); Tue, 03 Dec 2013 09:27:13 -0700 (MST) Cc: "Mike." , freebsd-questions@freebsd.org X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Dec 2013 16:27:15 -0000 On Tue, 3 Dec 2013, Julien Cigar wrote: > On Mon, Dec 02, 2013 at 08:56:13AM -0700, Warren Block wrote: >> On Mon, 2 Dec 2013, Julien Cigar wrote: >> >>> If you want to use GPT with gmirror you may want to mirror each >>> partition instead of the whole disk. >>> >>> For example on my box I have the following: https://dpaste.de/Rb3S >> >> There are a couple of potential problems with that. The big one is when >> a disk fails and is replaced. If you're not careful, the rebuild of all >> those mirrored partitions will start at the same time. Head contention >> will bring that to a near-standstill. It also puts a heavy load on the >> drive that still works. Hopefully it is not the same model and age as >> the one that failed, or its "warranty timer" may also be close to >> expiring. > > That's true, I turned off autosynchronization of stale components to > avoid this kind of bad scenario .. > >> >> A less-serious problem is that only the partitions are mirrored. That >> leaves out metadata like the partition tables and bootcode, but those >> typically do not change very often and might not be a problem. The >> admin has to remember to manually install such things on a new >> replacement disk, though. > > It's just a matter of gpart backup / gpart restore, right ? That will get the partition tables but not the bootcode or PMBR. A failed disk could then leave a mirror which has all the data but is unbootable. At some point, we'll have to address the conflict between gmirror and GPT. ZFS mirrors can replace gmirror in some situations, but not all.