From owner-freebsd-fs@FreeBSD.ORG Fri Jan 1 06:48:07 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 A7B441065698 for ; Fri, 1 Jan 2010 06:48:07 +0000 (UTC) (envelope-from danny@dannysplace.net) Received: from mail.dannysplace.net (mail.dannysplace.net [80.69.71.124]) by mx1.freebsd.org (Postfix) with ESMTP id 5D9AA8FC17 for ; Fri, 1 Jan 2010 06:48:07 +0000 (UTC) Received: from nas.lan ([203.206.171.212] helo=[192.168.10.10]) by mail.dannysplace.net with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.69 (FreeBSD)) (envelope-from ) id 1NQayV-000JIi-BW; Fri, 01 Jan 2010 16:27:03 +1000 Message-ID: <4B3D95AD.8050304@dannysplace.net> Date: Fri, 01 Jan 2010 16:26:53 +1000 From: Danny Carroll User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.1.5) Gecko/20091204 Thunderbird/3.0 MIME-Version: 1.0 To: Matt Simerson References: <568624531.20091215163420@pyro.de> <42952D86-6B4D-49A3-8E4F-7A1A53A954C2@spry.com> <957649379.20091216005253@pyro.de> <26F8D203-A923-47D3-9935-BE4BC6DA09B7@corp.spry.com> In-Reply-To: <26F8D203-A923-47D3-9935-BE4BC6DA09B7@corp.spry.com> X-Enigmail-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Authenticated-User: danny X-Authenticator: plain X-Sender-Verify: SUCCEEDED (sender exists & accepts mail) X-Exim-Version: 4.69 (build at 13-Aug-2009 20:22:24) X-Date: 2010-01-01 16:27:03 X-Connected-IP: 203.206.171.212:50080 X-Message-Linecount: 36 X-Body-Linecount: 22 X-Message-Size: 1681 X-Body-Size: 946 X-Received-Count: 1 X-Recipient-Count: 3 X-Local-Recipient-Count: 3 X-Local-Recipient-Defer-Count: 0 X-Local-Recipient-Fail-Count: 0 X-SA-Exim-Connect-IP: 203.206.171.212 X-SA-Exim-Rcpt-To: matt@corp.spry.com, solon@pyro.de, freebsd-fs@freebsd.org X-SA-Exim-Mail-From: danny@dannysplace.net X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on ferrari.dannysplace.net X-Spam-Level: * X-Spam-Status: No, score=1.8 required=8.0 tests=ALL_TRUSTED,AWL, FH_DATE_PAST_20XX autolearn=disabled version=3.2.5 X-SA-Exim-Version: 4.2 X-SA-Exim-Scanned: Yes (on mail.dannysplace.net) 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 06:48:07 -0000 On 17/12/2009 6:43 AM, Matt Simerson wrote: > Why would I bother? Both ways present each disk to FreeBSD. Based on > my understanding (and an answer received from Areca support), the only > reason I'd bother manually configuring some disks for passthrough is > if I wanted to use some disks in a RAID array and others as raw disks. > Configuring JBOD mode configures ALL the disks on the controller as > passthrough devices. > It's my experience that the statement above is simply not true. I confirmed this with throughput tests as well as talking to Areca (as I understand you also did). JBOD = Give the OS the drive. PassThrough = Give the OS the drive but run it through the cache first. I use passthrough specifically for this reason. If I lose power, then the cache should fix up the writes at restart. You do not have this protection when ZFS has access to the raw devices. Even worse if the devices write cache is turned on. -D