From owner-freebsd-fs@FreeBSD.ORG Sun Jan 27 13:01:42 2013 Return-Path: Delivered-To: fs@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id CF35BFA8 for ; Sun, 27 Jan 2013 13:01:42 +0000 (UTC) (envelope-from nowakpl@platinum.linux.pl) Received: from platinum.linux.pl (platinum.edu.pl [81.161.192.4]) by mx1.freebsd.org (Postfix) with ESMTP id 94985F4A for ; Sun, 27 Jan 2013 13:01:42 +0000 (UTC) Received: by platinum.linux.pl (Postfix, from userid 87) id 6918947E11; Sun, 27 Jan 2013 14:01:40 +0100 (CET) X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on platinum.linux.pl X-Spam-Level: X-Spam-Status: No, score=-1.4 required=3.0 tests=ALL_TRUSTED,AWL autolearn=disabled version=3.3.2 Received: from [10.255.0.2] (unknown [83.151.38.73]) by platinum.linux.pl (Postfix) with ESMTPA id E537F47DE6 for ; Sun, 27 Jan 2013 14:01:39 +0100 (CET) Message-ID: <5105252D.6060502@platinum.linux.pl> Date: Sun, 27 Jan 2013 14:01:33 +0100 From: Adam Nowacki User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 MIME-Version: 1.0 To: fs@FreeBSD.org Subject: RAID-Z wasted space - asize roundups to nparity +1 Content-Type: text/plain; charset=ISO-8859-2; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 27 Jan 2013 13:01:42 -0000 I've just found something very weird in the ZFS code. sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_raidz.c:504 in HEAD Can someone explain the reason behind this line of code? What it does is align on-disk record size to a multiple of number of parity disks + 1 ... this really doesn't make any sense. So far as I can tell those extra sectors are just padding - completely unused. For the array I'm using this results in 4.8% of wasted disk space - 1.7TB. It's a 12x 3TB disk RAID-Z2.