From owner-freebsd-hardware@FreeBSD.ORG Thu Nov 13 20:59:43 2008 Return-Path: Delivered-To: freebsd-hardware@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7B3F51065674; Thu, 13 Nov 2008 20:59:43 +0000 (UTC) (envelope-from fbsd@dannysplace.net) Received: from mail.dannysplace.net (mail.dannysplace.net [213.133.54.210]) by mx1.freebsd.org (Postfix) with ESMTP id 2BF858FC0A; Thu, 13 Nov 2008 20:59:43 +0000 (UTC) (envelope-from fbsd@dannysplace.net) Received: from 203-206-171-212.perm.iinet.net.au ([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 1L0jHv-000L89-BJ; Fri, 14 Nov 2008 06:59:41 +1000 Message-ID: <491C9535.3030504@dannysplace.net> Date: Fri, 14 Nov 2008 06:59:33 +1000 From: Danny Carroll User-Agent: Thunderbird 2.0.0.17 (Windows/20080914) MIME-Version: 1.0 To: Scott Long References: <490A782F.9060406@dannysplace.net> <20081031033208.GA21220@icarus.home.lan> <490A849C.7030009@dannysplace.net> <20081031043412.GA22289@icarus.home.lan> <490A8FAD.8060009@dannysplace.net> <491BBF38.9010908@dannysplace.net> <491C5AA7.1030004@samsco.org> In-Reply-To: <491C5AA7.1030004@samsco.org> 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 08-Jul-2008 08:59:40) X-Date: 2008-11-14 06:59:39 X-Connected-IP: 203.206.171.212:1171 X-Message-Linecount: 44 X-Body-Linecount: 29 X-Message-Size: 2326 X-Body-Size: 1532 X-Received-Count: 1 X-Recipient-Count: 4 X-Local-Recipient-Count: 4 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: scottl@samsco.org, freebsd-fs@freebsd.org, koitsu@freebsd.org, freebsd-hardware@freebsd.org X-SA-Exim-Mail-From: fbsd@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=0.2 required=8.0 tests=ALL_TRUSTED,TVD_RCVD_IP 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, Jeremy Chadwick , freebsd-hardware@freebsd.org Subject: Re: Areca vs. ZFS performance testing. X-BeenThere: freebsd-hardware@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: fbsd@dannysplace.net List-Id: General discussion of FreeBSD hardware List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 13 Nov 2008 20:59:43 -0000 Scott Long wrote: > The Areca controller likely doesn't buffer/cache for disks in JBOD mode, > as others in this thread have stated. Without buffering, simple disk > controllers will almost always be faster than accelerated raid > controllers because the accelerated controllers add more latency between > the host and the disk. A simple controller will directly funnel data > from the host to the disk as soon as it receives a command. An > accelerated controller, however, has a CPU and a mini-OS on it that has > to schedule the work coming from the host and handle its own tasks and > interrupts. This adds latency that quickly adds up under benchmarks. > Your numbers clearly demonstrate this. That's nice to know. I'm not sure it tells us why the Non-Cached writes were about 8% faster though. The other thing about the "NoWriteCache" test I performed that I neglected to mention yesterday is that I actually panic'd the box (running out of memory). This was the first time I have had that happen with ZFS even though in previous testing (with cache enabled) I punished the box for a lot longer. Perhaps the ZFS caching took over where the disk caching left off? Could that explain why I did not see a negative difference in the numbers between Cache enabled and Cache disabled? One of the questions I wanted to answer for myself was just this: "Does a battery-backed cache on an Areca card protect me when I am in JBOD mode." If the Areca does not buffer/cache in JBOD mode then that means the answer is no. -D