From owner-freebsd-fs@FreeBSD.ORG Fri Apr 24 06:52:01 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 142831065678 for ; Fri, 24 Apr 2009 06:52:01 +0000 (UTC) (envelope-from scott@bqinternet.com) Received: from mail.bqinternet.com (mail.bqinternet.com [69.9.32.203]) by mx1.freebsd.org (Postfix) with ESMTP id DE69B8FC1A for ; Fri, 24 Apr 2009 06:52:00 +0000 (UTC) (envelope-from scott@bqinternet.com) Received: from localhost (mail [69.9.32.203]) by mail.bqinternet.com (Postfix) with ESMTP id AF16E409990; Fri, 24 Apr 2009 06:52:01 +0000 (GMT) Received: from mail.bqinternet.com ([69.9.32.203]) by localhost (mail.bqinternet.com [69.9.32.203]) (amavisd-new, port 10024) with ESMTP id ytgzG+E7142L; Fri, 24 Apr 2009 06:52:01 +0000 (GMT) Received: from scott-burnss-macbook-air.local (mail [69.9.32.203]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.bqinternet.com (Postfix) with ESMTP id 81A2D40998B; Fri, 24 Apr 2009 06:52:00 +0000 (GMT) Message-ID: <49F1618E.3080208@bqinternet.com> Date: Fri, 24 Apr 2009 02:51:58 -0400 From: Scott Burns User-Agent: Thunderbird 2.0.0.21 (Macintosh/20090302) MIME-Version: 1.0 To: Andrew Snow References: <49F048FB.6000401@bqinternet.com> <20090423195335.521db0a7@kan.dnsalias.net> <49F10660.201@modulus.org> In-Reply-To: <49F10660.201@modulus.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-fs@freebsd.org Subject: Re: UFS2 metadata checksums 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, 24 Apr 2009 06:52:01 -0000 Andrew Snow wrote: > > Ideally you would implement complete disk checksumming as a GEOM device. > > Then you could layer geom_mirror on top of it, so that if the checksum > fails and returns EIO, geom_mirror can try the alternate device and > rebuild the one with the bad checksums. > > That will then complete the feature set implemented by ZFS, but for any > filesystem on top of GEOM. > > - Andrew > The geli(8) GEOM class is able to verify sectors (and I believe it returns EINVAL on ones that fail), but with a noticeable performance impact. I could certainly see the use for a GEOM class that just does simple checksumming. If gmirror can then be aware of it, that does provide functionality similar to a ZFS mirror. -- Scott Burns System Administrator BQ Internet Corporation