From owner-freebsd-stable@FreeBSD.ORG Sun Mar 30 09:01:23 2003 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1805837B401 for ; Sun, 30 Mar 2003 09:01:23 -0800 (PST) Received: from out004.verizon.net (out004pub.verizon.net [206.46.170.142]) by mx1.FreeBSD.org (Postfix) with ESMTP id 46E4A43FE9 for ; Sun, 30 Mar 2003 09:01:22 -0800 (PST) (envelope-from cswiger@mac.com) Received: from mac.com ([129.44.43.88]) by out004.verizon.net (InterMail vM.5.01.05.27 201-253-122-126-127-20021220) with ESMTP id <20030330170121.UFYD10550.out004.verizon.net@mac.com>; Sun, 30 Mar 2003 11:01:21 -0600 Message-ID: <3E8722DD.5050703@mac.com> Date: Sun, 30 Mar 2003 12:01:17 -0500 From: Chuck Swiger Organization: The Courts of Chaos User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.3) Gecko/20030312 X-Accept-Language: en-us, en MIME-Version: 1.0 To: freebsd-stable@freebsd.org References: <20030330125138.K23911@leelou.in.tern> <3E870CC7.5000204@mac.com> <20030330175605.E23911@leelou.in.tern> In-Reply-To: <20030330175605.E23911@leelou.in.tern> X-Enigmail-Version: 0.73.1.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Authentication-Info: Submitted using SMTP AUTH at out004.verizon.net from [129.44.43.88] at Sun, 30 Mar 2003 11:01:21 -0600 cc: Lukas Ertl Subject: Re: vinum performance X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 30 Mar 2003 17:01:54 -0000 Lukas Ertl wrote: [ ... ] >> There are three goals or priorities to choose from when configuring >> RAID: performance, reliability, and cost. What are yours? > > I just wanted to test the performance of these drives and of vinum; I had > no goals to reach. Testing something to see what happens is a goal in and of itself. Nevertheless, my question wasn't idle: you probably will find that if you choose a goal like, "I want to set up a RAID volume that has really good performance", that you learn more from your testing. >> Also, what tasks you intend to use the RAID filesystem for are critical >> to consider, even if the answer is simply "undifferentiated >> general-purpose storage". In particular, RAID-5 write performance is >> going to be slow, even with RAID hardware support which offloads the >> parity calculations from the system CPU(s). RAID-5 is best suited for >> read-mostly or read-only volumes, where you value cost more than >> performance. > > Ok. But I still don't understand why RAID 5 write performance is _so_ bad. RAID-5 trades performance for both cost and for reliability. Actually, most forms of RAID trade performance OR cost for reliability, but RAID-5 does both and thus is generally slower than a single drive. Especially when you're got lots of multithreaded small writes; that is to say, doing an I/O benchmark, which is designed to saturate the I/O system deliberately, and tends to have an even balance of reads to writes, is pretty much a worst-case usage scenario for RAID-5. That doesn't mean that RAID-5 isn't useful, and it can perform okay under light to moderate I/O loads, but RAID-5 degrades badly under high write loads. > The CPU is not the bottle neck, it's rather bored. And I don't understand > why RAID 0 doesn't give a big boost at all. Is the ahc driver known to be > slow? FreeBSD supports Adaptec hardware very well, in general. Or is that vice versa? >> Um, that is a dual-channel card, and you're splitting drives onto both >> channels, right? > > Yes, it is dual channel, but the disks I'm testing are all connected to > the same channel. Bad layout? Highly non-optimal?, depending on how you wish to look at it. :-) -- -Chuck PS: You should also consider what happens if a drive fails; what happens to the performance then? If you've got hot-swappable hardware, try yanking a disk or two...