From owner-freebsd-doc@FreeBSD.ORG Thu May 17 21:17:31 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 02527106564A for ; Thu, 17 May 2012 21:17:31 +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 B55808FC15 for ; Thu, 17 May 2012 21:17:30 +0000 (UTC) Received: from wonkity.com (localhost [127.0.0.1]) by wonkity.com (8.14.5/8.14.5) with ESMTP id q4HLHTXp061820 for ; Thu, 17 May 2012 15:17:29 -0600 (MDT) (envelope-from wblock@wonkity.com) Received: from localhost (wblock@localhost) by wonkity.com (8.14.5/8.14.5/Submit) with ESMTP id q4HLHTUY061817 for ; Thu, 17 May 2012 15:17:29 -0600 (MDT) (envelope-from wblock@wonkity.com) Date: Thu, 17 May 2012 15:17:29 -0600 (MDT) From: Warren Block To: doc@freebsd.org Message-ID: User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (wonkity.com [127.0.0.1]); Thu, 17 May 2012 15:17:30 -0600 (MDT) Cc: Subject: 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: Thu, 17 May 2012 21:17:31 -0000 Summary: Handbook mirror example broken, new rewrite here, feedback desired before commit. http://www.wonkity.com/~wblock/mirror/book.html http://www.wonkity.com/~wblock/mirror/chapter.diff More detail: The existing mirroring section in the GEOM chapter of the Handbook uses a workaround to add another drive and make a mirror with one existing drive without moving data. http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html That workaround creates mirrors that FreeBSD 9 and later versions of 8 see as having invalid, overlapping areas. The more strict tests prevent at least FreeBSD 9 from even booting from mirrors created that way: http://www.freebsd.org/releases/9.0R/relnotes-detailed.html#AEN1277 Ideally, the procedure would be able to create a single-drive mirror but use only a limited amount of disk space on the new drive, making that space the same size as the existing drive. (Here's a new 80G drive, but I only want to use 40G of space for the mirror.) Of course this can be done with partitions, but that is more complex and there may be thrashing issues with multiple partitions. It turns out to be fairly difficult to do this in a situation that will work reliably for the average user. I've rewritten the mirroring section to just use two new drives. A mirror *can* be created with two different-sized drives, provided they are both seen at the time of creation. The smaller size is used; exposing that size with a command-line option would be very useful.