From owner-freebsd-questions@freebsd.org Thu Aug 31 01:00:03 2017 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 6151EE0E44D for ; Thu, 31 Aug 2017 01:00:03 +0000 (UTC) (envelope-from wblock@wonkity.com) Received: from wonkity.com (wonkity.com [67.158.26.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "wonkity.com", Issuer "wonkity.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 3486C24FD for ; Thu, 31 Aug 2017 01:00:02 +0000 (UTC) (envelope-from wblock@wonkity.com) Received: from wonkity.com (localhost [127.0.0.1]) by wonkity.com (8.15.2/8.15.2) with ESMTPS id v7V0xs2K028426 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 30 Aug 2017 18:59:54 -0600 (MDT) (envelope-from wblock@wonkity.com) Received: from localhost (wblock@localhost) by wonkity.com (8.15.2/8.15.2/Submit) with ESMTP id v7V0xsEt028423; Wed, 30 Aug 2017 18:59:54 -0600 (MDT) (envelope-from wblock@wonkity.com) Date: Wed, 30 Aug 2017 18:59:54 -0600 (MDT) From: Warren Block To: Frank Leonhardt cc: freebsd-questions@freebsd.org Subject: Re: help creating new gmirror > 2TB In-Reply-To: <26f5e88e-1ea7-6332-ca5e-f055cfbdd280@fjl.co.uk> Message-ID: References: <26f5e88e-1ea7-6332-ca5e-f055cfbdd280@fjl.co.uk> User-Agent: Alpine 2.21 (BSF 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (wonkity.com [127.0.0.1]); Wed, 30 Aug 2017 18:59:54 -0600 (MDT) X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 31 Aug 2017 01:00:03 -0000 On Wed, 30 Aug 2017, Frank Leonhardt wrote: > On 29/08/2017 21:12, William Dudley wrote: >> Hi, >> >> I want to create a simple mirror > 2TB on a FreeBSD 10.3 system. >> >> I have 2 identical 4TB disks. >> >> The examples in freebsd handbook "geom-mirror" pages show creation of a 2TB >> mirror using >> MBR partitioning, and that has an upper limit of 2TB. >> >> Some documentation says not to use GPT partitioning with gmirror because >> both store their information in the last sector on the disk. >> >> I'm not expert enough to be able to solve this myself. >> >> How do I create a gmirror of 4TB size? >> >> I want to partition it into 4 slices after I create it, but think I can use >> gpart to do that. >> >> Note: I'm not interested in using zfs unless there's no way to do this with >> gmirror. >> I read too many zfs failure stories on this mailing list to be comfortable >> with zfs. > > I still get a bit worried about this, but I'm 99.9% sure you'll be okay with > MBR assuming it's an AFD (4K sector drive). The bodge/workaround works. If > it's SAS instead of SATA, all bets are off. > > Although I use ZFS a lot, I still prefer geom mirror for twin-disk systems. I > feel a lot more comfortable booting from it in the event of a failure. ZFS > has its good points, but so does UFS. > > Trying to get geom mirror to work with GPT as it stands just leads to pain. > I've taken a look at the code with a view to fixing this is no one else does, > but UFS is so un-cool in most circles and I don't fancy doing it alone in > case I zap someone's data. it doesn't look that tricky to move the metadata > somewhere else, and by checking for a GPT you can select between the old/new > block. It's unexpected interactions I'm worried about. At some point in the last couple of years, hrs@ produced a working patch which did something like that, although I don't remember the details. It moved either the GPT backup table or the gmirror metadata. It was turned down as breaking standards.