From owner-freebsd-current@FreeBSD.ORG Fri Nov 13 02:51:34 2009 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E8B1F1065670 for ; Fri, 13 Nov 2009 02:51:34 +0000 (UTC) (envelope-from james-freebsd-current@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 0210D8FC17 for ; Fri, 13 Nov 2009 02:51:33 +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 nAD2pUWx024027; Thu, 12 Nov 2009 20:51:32 -0600 (CST) (envelope-from james-freebsd-current@jrv.org) Authentication-Results: mail.jrv.org; domainkeys=pass (testing) header.from=james-freebsd-current@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:to:cc:subject: references:in-reply-to:content-type:content-transfer-encoding; b=LZjxScRLWtVvl8+sDaiU6x1GcukvouJdIWl2rUkTUNqZzBY35N8/byQEB2qDHaUa9 xuI7vUe4burTWm0EE8zClRten57Q0OaEegG9t61E8e+2NOJR4eT7SHV5Yq30e1JyOP8 J2MobkMayivIz8/AVhiuRkkgwTVjj4mB+86a7OU= Message-ID: <4AFCC9B2.2050401@jrv.org> Date: Thu, 12 Nov 2009 20:51:30 -0600 From: "James R. Van Artsdalen" User-Agent: Thunderbird 2.0.0.23 (Macintosh/20090812) MIME-Version: 1.0 To: Artem Belevich References: <11167f520911111050j36dd94far667c81e6f5c18e69@mail.gmail.com> <20091111204903.GI89052@dan.emsphone.com> <11167f520911111326v13bb442bt36e853afbecdf834@mail.gmail.com> <9bbcef730911111352t12188bdajbca71bcf35a5beb5@mail.gmail.com> <11167f520911121044l74744c30u5a4d9ca008ab863c@mail.gmail.com> <11167f520911121101o403751ddmb544dfaf1c61bf1e@mail.gmail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: freebsd-current@freebsd.org Subject: Re: Help ZFS FreeBSD 8.0 RC2 Write performance issue X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Nov 2009 02:51:35 -0000 Artem Belevich wrote: > Log seems to be somewhat weak point in ZFS. If you lose your log > device, you will lose your pool. In ZFS losing *any* vdev causes a pool to fault! The log vdev is no different and is not a weak point in that regard. In ZFS *every* vdev should be redundant. In the case of a log this means a MIRROR since a log cannot be a RAIDZ. That's not a big deal since you really should put the MIRROR disks on different controllers, and preferably using different drives, independent cables & power supplies, etc. (I think a cache vdev is different and need not be reliable, but I have not tested to see what happens if it is not present when the pool is imported) The ZIL may have bugs but it's a very important feature to have, necessary in a transactional filesystem. A mythical "zfsck" program could probably wipe out the ZIL allowing the pool to import from the most recent uberblock state and losing a few seconds of sync's, better than nothing. Tricking ZFS into importing a pool with the log vdev missing is probably harder. > I'd say that SSD are probably the best fit for slog role. A PCI-e SSD like the OCZ P84 with sustained writes "up to" 600 MB/s might be a possibility for a high-throughput database server, if it uses an interface we have a driver for.