From owner-freebsd-fs@FreeBSD.ORG Fri Jan 1 21:45:28 2010 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 19ECA106566B for ; Fri, 1 Jan 2010 21:45:28 +0000 (UTC) (envelope-from bfriesen@simple.dallas.tx.us) Received: from blade.simplesystems.org (blade.simplesystems.org [65.66.246.74]) by mx1.freebsd.org (Postfix) with ESMTP id D46358FC17 for ; Fri, 1 Jan 2010 21:45:27 +0000 (UTC) Received: from freddy.simplesystems.org (freddy.simplesystems.org [65.66.246.65]) by blade.simplesystems.org (8.13.8+Sun/8.13.8) with ESMTP id o01LjJgD019402; Fri, 1 Jan 2010 15:45:19 -0600 (CST) Date: Fri, 1 Jan 2010 15:45:19 -0600 (CST) From: Bob Friesenhahn X-X-Sender: bfriesen@freddy.simplesystems.org To: "ticso@cicely.de" In-Reply-To: <20100101204752.GW43739@cicely7.cicely.de> Message-ID: References: <55389.88569.qm@web112405.mail.gq1.yahoo.com> <20100101204752.GW43739@cicely7.cicely.de> User-Agent: Alpine 2.01 (GSO 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (blade.simplesystems.org [65.66.246.90]); Fri, 01 Jan 2010 15:45:20 -0600 (CST) Cc: "freebsd-fs@freebsd.org" 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, 01 Jan 2010 21:45:28 -0000 On Fri, 1 Jan 2010, Bernd Walter wrote: > > Everyone do this if the board dies and needs replacement. > Not willingly, but it happens. > And what about zfs export - relocate disks to another machine - and > zfs import - without halt? > It is less safe if a cache flush won't flush its cache. > The real purpose to have buffered cache is to handle asyncronity in > RAID systems after power failure, but RAIDZ won't have this problem > by design, at least if running with CRC enabled. A proper write-through cache should automatically commit itself (in order) to backing store within a second or two. Other than cache designs which are not "proper" (which we should not use) the main concern is if the system loses power or crashes while it is producing a significant write load so that there is uncomitted data in cache. ZFS is not particularly more likely to lose user data, but it is much more likely to detect and report loss since most other filesystems don't even check, or even have a way to check. Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/