From owner-freebsd-fs@FreeBSD.ORG Fri Dec 18 19:10:51 2009 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 224BA106566C for ; Fri, 18 Dec 2009 19:10:51 +0000 (UTC) (envelope-from ticso@cicely7.cicely.de) Received: from raven.bwct.de (raven.bwct.de [85.159.14.73]) by mx1.freebsd.org (Postfix) with ESMTP id A3A4B8FC08 for ; Fri, 18 Dec 2009 19:10:50 +0000 (UTC) Received: from cicely5.cicely.de ([10.1.1.7]) by raven.bwct.de (8.13.4/8.13.4) with ESMTP id nBIItYZG071615 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 18 Dec 2009 19:55:34 +0100 (CET) (envelope-from ticso@cicely7.cicely.de) Received: from cicely7.cicely.de (cicely7.cicely.de [10.1.1.9]) by cicely5.cicely.de (8.14.2/8.14.2) with ESMTP id nBIItVoa016397 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 18 Dec 2009 19:55:31 +0100 (CET) (envelope-from ticso@cicely7.cicely.de) Received: from cicely7.cicely.de (localhost [127.0.0.1]) by cicely7.cicely.de (8.14.2/8.14.2) with ESMTP id nBIItU8h002929; Fri, 18 Dec 2009 19:55:30 +0100 (CET) (envelope-from ticso@cicely7.cicely.de) Received: (from ticso@localhost) by cicely7.cicely.de (8.14.2/8.14.2/Submit) id nBIItUGD002928; Fri, 18 Dec 2009 19:55:30 +0100 (CET) (envelope-from ticso) Date: Fri, 18 Dec 2009 19:55:30 +0100 From: Bernd Walter To: "James R. Van Artsdalen" Message-ID: <20091218185529.GC1531@cicely7.cicely.de> References: <568624531.20091215163420@pyro.de> <42952D86-6B4D-49A3-8E4F-7A1A53A954C2@spry.com> <957649379.20091216005253@pyro.de> <26F8D203-A923-47D3-9935-BE4BC6DA09B7@corp.spry.com> <4B299CEA.3070705@jrv.org> <4B2B9F82.4020909@jrv.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B2B9F82.4020909@jrv.org> X-Operating-System: FreeBSD cicely7.cicely.de 7.0-STABLE i386 User-Agent: Mutt/1.5.11 X-Spam-Status: No, score=-4.4 required=5.0 tests=ALL_TRUSTED=-1.8, AWL=0.019, BAYES_00=-2.599 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on spamd.cicely.de Cc: freebsd-fs Subject: Re: ZFS RaidZ2 with 24 drives? X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: ticso@cicely.de List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Dec 2009 19:10:51 -0000 On Fri, Dec 18, 2009 at 09:28:02AM -0600, James R. Van Artsdalen wrote: > Thomas Burgess wrote: > > One thing most people don't know about hard drives in general is that > > sometimes up to 30% of the space is actually ECC. With software raid > > systems like ZFS, this will eventually be somethign that we can take > > advantage of. > > ECC is less than 10% of the space. The inter-sector gap and gap between > a sector's address and data fields, etc, are larger and more problematic > as rotation speeds increase. > > > Because of this, you can imagine a scenario where allowing ZFS to > > use this ECC space as raw storage, while leaving the data corrections > > to ZFS would be ideal. It's not only a matter of space, it will also > > lead to nice improvements in speed. (more data can be read/written by > > the head as it passes) I can imagine this might work, but do not see it to be very realistic. And I'm not sure this is a very good idea as well. > The disk drive industry's solution to this is 4K sector sizes. See > http://www.anandtech.com/storage/showdoc.aspx?i=3691 This is an quite interesting article, but for me not very surprising. It is a bit more surprising that this is not already standard. The whole thing is not new - the Commodore 1581 floppy drive did a track at once logic with caching and supplied logical 256 Byte sectors with underlying 512 MFM blocks. With flash cards 4k physical sectors are also very common and writing smaller/unaligned transfers leads to slow read-modify-write cycles. You need to be very carefull when partitioning a flash based memory card - a lot of us are already using flash based as an alternative to an HDD. People also used MO media with 1k and 2k hard sectoring - they usually don't have an emulation for 512 Bytes. -- B.Walter http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.