From owner-freebsd-fs@freebsd.org Tue May 17 19:04:27 2016 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id C5A8BB3E25C for ; Tue, 17 May 2016 19:04:27 +0000 (UTC) (envelope-from brandon.wandersee@gmail.com) Received: from mail-ig0-f171.google.com (mail-ig0-f171.google.com [209.85.213.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 9D71918CF for ; Tue, 17 May 2016 19:04:27 +0000 (UTC) (envelope-from brandon.wandersee@gmail.com) Received: by mail-ig0-f171.google.com with SMTP id bi2so80216550igb.0 for ; Tue, 17 May 2016 12:04:27 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version; bh=qXUBYXlS1mLmujjk3kms9ENcUdPNe0C8oGEQ3MbMq98=; b=Zg9rue/4lvyDuFeNQ0FGZ/ixCw6ridrbh/suV4sMFRo8kVoEZ/HLTvyhfURAIIZpCq kbwz1DerbeXM1dQrgrMqLKwmnt59wUe1/UZg8dAFHLO4G+OHs0D+sv9k6Cz48irLmXs/ WcDeTyQr/vNEAxaPlD0/HNCjjDV9Y8WBAbMq3HT7VbQGoVGHThAnFZs3yIHOrT6vretO h+hqogtAI3tiCgf6kGICcui6oR5nnwNk/euQA4FqoDvMjVlulzNRXe4zLNaUAxcERBU2 +IC/a7gOguN1B0C1FqRTBskUNEzvpX2bR1NwF14Z05G5DQJhXUahz4sAurqZr5H11JT7 9pgg== X-Gm-Message-State: AOPr4FUYo2MOQpD7EUwUYvYARaODmRIs1hD35K4MNJDXZxh3abFttmTuZ622nk4Lj8Yc3g== X-Received: by 10.50.140.193 with SMTP id ri1mr15275060igb.60.1463511861711; Tue, 17 May 2016 12:04:21 -0700 (PDT) Received: from WorkBox.Home.gmail.com (97-116-8-66.mpls.qwest.net. [97.116.8.66]) by smtp.gmail.com with ESMTPSA id g186sm1478399iof.27.2016.05.17.12.04.19 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 May 2016 12:04:20 -0700 (PDT) References: <8441f4c0-f8d1-f540-b928-7ae60998ba8e@lexa.ru> <16e474da-6b20-2e51-9981-3c262eaff350@lexa.ru> <1e012e43-a49b-6923-3f0a-ee77a5c8fa70@lexa.ru> User-agent: mu4e 0.9.16; emacs 24.5.1 From: Brandon J. Wandersee To: Alex Tutubalin Cc: freebsd-fs@freebsd.org Subject: Re: ZFS performance bottlenecks: CPU or RAM or anything else? In-reply-to: <1e012e43-a49b-6923-3f0a-ee77a5c8fa70@lexa.ru> Date: Tue, 17 May 2016 14:04:18 -0500 Message-ID: <86shxgsdzh.fsf@WorkBox.Home> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 17 May 2016 19:04:27 -0000 Alex Tutubalin writes: > On 5/17/2016 3:29 PM, Daniel Kalchev wrote: > >> Not true. You can have N-way mirror and it will survive N-1 drive failures. > I agree, but 3-way mirror does not looks economical compared to raidz2. If you're already planning for multiple simultaneous drive failures, "economical" isn't really a factor, is it? Those disks have to get replaced regardless of the redundancy scheme you assign to them. ;) Whether the concern is performance or capacity, mirrors will offer the most flexibility. Increasing either the performance or capacity of a RAIDZ pool necessitates either replacing every disk in the pool or doubling the number of disks in the pool, all at once. Mirrors allow you to grow a pool and increase/decrease redundancy asymmetrically. True, four disks in a two-mirror stripe will see you restoring a backup if one disk from each mirror dies, but (arguably) six disks in a two-mirror stripe offer both better redundancy and better performance. Speaking strictly about performance, RAIDZ performance is pretty much fixed, while mirrored performance will (I believe) increase slightly as you add disks and increase greatly as you add vdevs. -- :: Brandon J. Wandersee :: brandon.wandersee@gmail.com :: -------------------------------------------------- :: 'The best design is as little design as possible.' :: --- Dieter Rams ----------------------------------