From owner-freebsd-fs@FreeBSD.ORG Fri Dec 18 15:28:04 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 9AA691065676 for ; Fri, 18 Dec 2009 15:28:04 +0000 (UTC) (envelope-from james-freebsd-fs2@jrv.org) Received: from mail.jrv.org (adsl-70-243-84-13.dsl.austtx.swbell.net [70.243.84.13]) by mx1.freebsd.org (Postfix) with ESMTP id 3A5AE8FC15 for ; Fri, 18 Dec 2009 15:28:03 +0000 (UTC) Received: from kremvax.housenet.jrv (kremvax.housenet.jrv [192.168.3.124]) by mail.jrv.org (8.14.3/8.14.3) with ESMTP id nBIFS2FR088795; Fri, 18 Dec 2009 09:28:02 -0600 (CST) (envelope-from james-freebsd-fs2@jrv.org) Authentication-Results: mail.jrv.org; domainkeys=pass (testing) header.from=james-freebsd-fs2@jrv.org DomainKey-Signature: a=rsa-sha1; s=enigma; d=jrv.org; c=nofws; q=dns; h=message-id:date:from:user-agent:mime-version:cc:subject: references:in-reply-to:content-type:content-transfer-encoding; b=oGOYt5wTMadBqyEGdWvsV3IInRLrgNtNM/BYxKqF8s7dImarFQi9bh24wjePwti0T uOzLWiHQa2m4G4IVeRvvyU4cN0PQ7G7T+MdiXKffJeS9tQ+iIZ9yMF1o49wMJ0PfCYD sw/6z7ArbRIZgK/Djh9qrcCKJQu0itwE2/rGmD0= Message-ID: <4B2B9F82.4020909@jrv.org> Date: Fri, 18 Dec 2009 09:28:02 -0600 From: "James R. Van Artsdalen" User-Agent: Thunderbird 2.0.0.23 (Macintosh/20090812) MIME-Version: 1.0 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> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: freebsd-fs Subject: Re: ZFS RaidZ2 with 24 drives? X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Dec 2009 15:28:04 -0000 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) The disk drive industry's solution to this is 4K sector sizes. See http://www.anandtech.com/storage/showdoc.aspx?i=3691 Even ZFS would need major changes to use drives without ECC without an increased hard error rate. I don't see this happening since no filesystems exist yet for this environment, and since transitions to new filesystems are so slow (99.9%+ of systems today are running filesystems architectures at least two decades old).