From owner-freebsd-questions@FreeBSD.ORG Sat Feb 16 19:13:23 2013 Return-Path: Delivered-To: questions@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id A7F17D7B for ; Sat, 16 Feb 2013 19:13:23 +0000 (UTC) (envelope-from cpghost@cordula.ws) Received: from mail-da0-f49.google.com (mail-da0-f49.google.com [209.85.210.49]) by mx1.freebsd.org (Postfix) with ESMTP id 58F0F949 for ; Sat, 16 Feb 2013 19:13:23 +0000 (UTC) Received: by mail-da0-f49.google.com with SMTP id t11so1873330daj.22 for ; Sat, 16 Feb 2013 11:13:17 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:x-received:x-originating-ip:in-reply-to:references :date:message-id:subject:from:to:cc:content-type:x-gm-message-state; bh=I+XfvmN3249BUrQ0t5nJKFRfxmWZcS9BW7IgeP/Ec2k=; b=Po4oiroo8yftdtRCzgH7sVQEiRCanmvNwZ0vhYCvxkZw0QoaqxPIWqLk4npPVF203b Aw/S1XAuTiC/u1hA3NhfCXo0s2F5Exh92AFmEmr2RQvxksTWMzJLPVsUqms1hBXihbpQ +tH5bEaYfHpjHIf4Vg3ghvj5Vl9btG3NU72pj6vDLek57qPMICBgdXNnu2jKlq/eoeLd Br1t9sJN94J1Y05My9p4S01M/v9RSTaPhQncaz5UmSTjKYENUcNdXcRxLnd++IhJ4GKM 5NJ58mYWGWThCmg/LGtH+6m7PkO32ifTy2jtq5WsVgf1sXRRddJksfSAVG92lUeyo4FY gtZQ== MIME-Version: 1.0 X-Received: by 10.66.81.199 with SMTP id c7mr23048413pay.39.1361041553726; Sat, 16 Feb 2013 11:05:53 -0800 (PST) Received: by 10.68.76.195 with HTTP; Sat, 16 Feb 2013 11:05:53 -0800 (PST) X-Originating-IP: [93.221.168.254] In-Reply-To: <20130216183449.GD3070@schweikhardt.net> References: <20130216144751.GC3070@schweikhardt.net> <20130216183449.GD3070@schweikhardt.net> Date: Sat, 16 Feb 2013 20:05:53 +0100 Message-ID: Subject: Re: Should I bother with a gvinum stripe when using a pair of SSDs? From: "C. P. Ghost" To: Jens Schweikhardt Content-Type: text/plain; charset=ISO-8859-1 X-Gm-Message-State: ALoCoQnBvfTJpix0og+8qOZDiwiDA2S+EnpXrv7J97DEG5xNmwCh2vS/rUe3BC4V0oizxup4qMov Cc: questions@freebsd.org X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 16 Feb 2013 19:13:23 -0000 On Sat, Feb 16, 2013 at 7:34 PM, Jens Schweikhardt wrote: > On Sat, Feb 16, 2013 at 04:44:06PM +0100, C. P. Ghost wrote: > # On Sat, Feb 16, 2013 at 3:47 PM, Jens Schweikhardt > # wrote: > # > hello, world\n > # > > # > currently the only gvinum partition on my home system is a stripe for /home > # > across two Velociraptor HDDs. I'm thinking of replacing the HDDs with a > # > pair of SSDs. I was thinking of reducing complexity and in the migration > # > possibly no longer use gvinum at all--one less thing to configure and worry > # > about. > # > > # > * Would gvinum striping bring any speed advantage with a pair of SSDs? > # > * Or am I hitting other limits so that striping SSDs is a waste anyway? > # > * Should I finally take the plunge and acquaint myself with ZFS? > # > > # > System has 4GB RAM in an ASUS P5Q3 Deluxe with SATA II. It appears to me > # > that SATA II with 300MB/s is maxed out by a single SSD and striping it > # > will not improve r/w throughput. Is my simplistic reasoning correct? > # > # Jens, > # > # as always it depends on what you're trying to achieve: > # - max speed / lower latency? > # - max storage? > # - max redundancy? > # - max run-time-to-data-loss? > # > # Your choice of SSD probably means you'd like to reduce latency > # and maximize data throughput. > > Exactly, when I started vith vinum many years ago in the magnetic HD > age, striping with vinum gave me almost factor 2 in r/w speed as > measured with dd. (I do backups regularly to other media, so data > loss protection is not my primary concern). > > I realize that maximum SSD speeds as advertised by vendors and tests > (e.g. 520MB/s for contemporary top notch SSDs) may only be reached > under certain conditions far away from my normal usage, which is > re-building worlds and kernels and ports on a daily basis. So if for > my realworld working set a single SSD can deliver 300MB/s, striping > with vinum just might get me a factor 2 again to 600MB/s across > two SSDs. Then it would be worthwile to keep gvinum. > > Does that make sense? My understanding of SSD and SATA capabilities > may however be completely dreamed up... Assuming the right cables etc.., I *guess* the limiting factor would ultimately be the (AHCI-)SATA controller itself, or even the bus to which it is attached. Add to this that embedded DMA controllers may compete for the bus, limiting transfer rates even more. I don't know how such a setup scales; that's way too system dependent. If you have hard requirements w.r.t. latency and throughput, you'll ultimately have to run some real world tests on the target system. > Regards, > > Jens > -- > Jens Schweikhardt http://www.schweikhardt.net/ > SIGSIG -- signature too long (core dumped) -cpghost. -- Cordula's Web. http://www.cordula.ws/