From owner-freebsd-questions@FreeBSD.ORG Fri Jun 7 16:18:59 2013 Return-Path: Delivered-To: freebsd-questions@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 D45E95C3 for ; Fri, 7 Jun 2013 16:18:59 +0000 (UTC) (envelope-from dan@dan.emsphone.com) Received: from email2.allantgroup.com (email2.emsphone.com [199.67.51.116]) by mx1.freebsd.org (Postfix) with ESMTP id 922AB18B0 for ; Fri, 7 Jun 2013 16:18:58 +0000 (UTC) Received: from dan.emsphone.com (dan.emsphone.com [172.17.17.101]) by email2.allantgroup.com (8.14.5/8.14.5) with ESMTP id r57GIoEZ038432 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 7 Jun 2013 11:18:50 -0500 (CDT) (envelope-from dan@dan.emsphone.com) Received: from dan.emsphone.com (smmsp@localhost [127.0.0.1]) by dan.emsphone.com (8.14.7/8.14.6) with ESMTP id r57GIox5092268 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 7 Jun 2013 11:18:50 -0500 (CDT) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.14.7/8.14.6/Submit) id r57GIoxO092267; Fri, 7 Jun 2013 11:18:50 -0500 (CDT) (envelope-from dan) Date: Fri, 7 Jun 2013 11:18:50 -0500 From: Dan Nelson To: Quartz Subject: Re: ZFS: raid VS copies=n Message-ID: <20130607161850.GA37520@dan.emsphone.com> References: <51B201D4.3000705@sneakertech.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51B201D4.3000705@sneakertech.com> X-OS: FreeBSD 9.1-STABLE User-Agent: Mutt/1.5.21 (2010-09-15) X-Virus-Scanned: clamav-milter 0.97.8 at email2.allantgroup.com X-Virus-Status: Clean X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (email2.allantgroup.com [172.17.19.78]); Fri, 07 Jun 2013 11:18:50 -0500 (CDT) X-Spam-Status: No, score=-3.9 required=5.0 tests=ALL_TRUSTED,BAYES_00, RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on email2.allantgroup.com X-Scanned-By: MIMEDefang 2.73 Cc: FreeBSD questions X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 07 Jun 2013 16:18:59 -0000 In the last episode (Jun 07), Quartz said: > How does the ZFS option 'copies=n' and raid relate to and interact with > each other? specifically recovery in the event of a failure. For > example, is having three disks in a raid-1 configuration with copies=1 > effectively the same as having three disks in a raid-0 with copies=3? Are > the copies distributed uniformly across all drives in the pool, or > concentrated, or what? What happens with configs like a raid-z2 with > copies=2? Which / how many disks can you lose? The code will try to place the extra copies on different vdevs, but if that's not possible, it will try and place them at least 1/8th of the disk size apart on the same disk. Copies aren't meant to protect against whole disk loss, but more local damage within a disk. https://blogs.oracle.com/bill/entry/ditto_blocks_the_amazing_tape https://blogs.oracle.com/relling/entry/zfs_copies_and_data_protection -- Dan Nelson dnelson@allantgroup.com