From owner-freebsd-stable@FreeBSD.ORG Wed Sep 2 14:10:09 2009 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E4B801065670 for ; Wed, 2 Sep 2009 14:10:09 +0000 (UTC) (envelope-from dimitry@andric.com) Received: from tensor.andric.com (cl-327.ede-01.nl.sixxs.net [IPv6:2001:7b8:2ff:146::2]) by mx1.freebsd.org (Postfix) with ESMTP id A3C718FC13 for ; Wed, 2 Sep 2009 14:10:09 +0000 (UTC) Received: from [IPv6:2001:7b8:3a7:0:e817:f690:b95a:3ed2] (unknown [IPv6:2001:7b8:3a7:0:e817:f690:b95a:3ed2]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by tensor.andric.com (Postfix) with ESMTPSA id 947A55C59; Wed, 2 Sep 2009 16:10:08 +0200 (CEST) Message-ID: <4A9E7CC3.1090605@andric.com> Date: Wed, 02 Sep 2009 16:10:11 +0200 From: Dimitry Andric User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; en-US; rv:1.9.1.4pre) Gecko/20090901 Shredder/3.0b4pre MIME-Version: 1.0 To: Mark Stapper References: <061541E3-F301-46C4-8ECB-5B05854F0EAA@exscape.org> <4A9D558A.9070609@quip.cz> <4A9E1CB5.6030906@mapper.nl> <20090902074445.GA13588@dmr.ath.cx> <4A9E2C7C.6030904@mapper.nl> In-Reply-To: <4A9E2C7C.6030904@mapper.nl> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: freebsd-stable@freebsd.org, Thomas Backman , Emil Mikulic , Miroslav Lachman <000.fbsd@quip.cz>, Maciej Jan Broniarz Subject: Re: zfs on gmirror slice X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 Sep 2009 14:10:10 -0000 On 2009-09-02 10:27, Mark Stapper wrote: > self-healing sounds very nice, but with mirrorring you have data on two > discs, so in that case there no "healing" involved, it's just > checksumming and reading the non-corrupted copy. > From the gmirror manpage: "All operations like failure detection, stale > component detection, rebuild of stale components, etc. are also done > automatically." > This would indicate the same functionality, with a much less fancy name. Not really. ZFS can checksum the actual file data, while gmirror can only detect errors it gets told about by the underlying disk. E.g. if the disk silently corrupts data, you will never know about it. Also, if gmirror needs to resynchronize, it must resynchronize the whole disk, since it can't detect which specific parts of it were corrupted. ZFS synchronizes on demand. There are also some other advantages to ZFS mirroring, see pages 15 and further of these slides: http://www.opensolaris.org/os/community/zfs/docs/zfs_last.pdf