From owner-freebsd-fs@freebsd.org Wed Aug 10 11:44:09 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 5DB1EBB5057 for ; Wed, 10 Aug 2016 11:44:09 +0000 (UTC) (envelope-from etnapierala@gmail.com) Received: from mail-wm0-x242.google.com (mail-wm0-x242.google.com [IPv6:2a00:1450:400c:c09::242]) (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 E4FB91D2F for ; Wed, 10 Aug 2016 11:44:08 +0000 (UTC) (envelope-from etnapierala@gmail.com) Received: by mail-wm0-x242.google.com with SMTP id o80so9012696wme.0 for ; Wed, 10 Aug 2016 04:44:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:date:from:to:cc:subject:message-id:mail-followup-to :references:mime-version:content-disposition:in-reply-to:user-agent; bh=P6XjQKNezTiKy/Z9OXe1vTCnCNi0NoRgJ99ZEgFPfzQ=; b=tavNiPHi3IYXPeQ2N56rjZFkEel8RNT1x6DW6Yq0b3jo0JDBqlQmcTKVxDZpFUTuQH NlfD82dxlUi2E11nJdhU0FKfrb2LIgPf0EXOquCsCIwShzEBTzyFiOPKRd49n1MDlR9I U+Wcr60GJ5ufAdUygIXeAV+8zQbdjWhkdtmxGaFl51hVCNQTa8xyStxTr9lBmRbt15dD zx8zJhrXrPgJS+FiNZmEacAPvSjUsOOMBhQWC1dQB1Qt9XMXcbW0pYwunfKkQMzvr3Sz wBjjNzIY3QSx20Yq6c0U0oydeu5YXTeX1xrc1WSECaKf50zP1BHubDgXm9iFNRrp2D73 mgaA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to:user-agent; bh=P6XjQKNezTiKy/Z9OXe1vTCnCNi0NoRgJ99ZEgFPfzQ=; b=iHp6svMQgAgRhehkmN2gDomHQCAEri5baKUETpBpQHNE6ytMuwsVJAvW3YVlgOOcPE 9Y2DZfjdBVXMaCX4NIgH2r6qyE6v0Qdd/H16XVMr1W5daP4POyAdjgM23TfSKRr10Z8K kVyhn2oFqQAhM5LyOn60PnCueNKxlGZTWetxPQquuMNeiNWKvTx1nd6apkntzc6onTfy 1AyzvQp3Mq9bk/EcO93d3Lo0ESe04UTHzlGLL09Nlhdx9cUjSTnVJcVcTH1aJ6sv9+LV /HE3QTJZgCUEMKiDHSm7xR9YZU2gkt+4Ig3hODd1eSYDqs9qu8QUWXiKDXrAJ1wLaNiH u0cQ== X-Gm-Message-State: AEkoouvV4V88Nw2Zluwj69PMF/Cx+3G+M8+Co64nlfKcKrbrqVX0KkpHpP9MVRdzmDCdMQ== X-Received: by 10.28.134.203 with SMTP id i194mr2919000wmd.22.1470829447510; Wed, 10 Aug 2016 04:44:07 -0700 (PDT) Received: from brick (abuf79.neoplus.adsl.tpnet.pl. [83.8.177.79]) by smtp.gmail.com with ESMTPSA id za2sm42607988wjb.34.2016.08.10.04.44.05 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Aug 2016 04:44:06 -0700 (PDT) Sender: =?UTF-8?Q?Edward_Tomasz_Napiera=C5=82a?= Date: Wed, 10 Aug 2016 13:44:04 +0200 From: Edward Tomasz =?utf-8?Q?Napiera=C5=82a?= To: Ben RUBSON Cc: freebsd-fs@freebsd.org Subject: Re: [iSCSI] Trying to reach max disk throughput Message-ID: <20160810114404.GA80485@brick> Mail-Followup-To: Ben RUBSON , freebsd-fs@freebsd.org References: <6B32251D-49B4-4E61-A5E8-08013B15C82B@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6B32251D-49B4-4E61-A5E8-08013B15C82B@gmail.com> User-Agent: Mutt/1.6.1 (2016-04-27) 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: Wed, 10 Aug 2016 11:44:09 -0000 On 0810T1154, Ben RUBSON wrote: > Hello, > > I'm facing something strange with iSCSI, I can't manage to reach the expected disk throughput using one (read or write) thread. [..] > ### Initiator : iscsi disk throughput : > > ## dd if=/dev/da8 of=/dev/null bs=$((128*1024)) count=81920 > 10737418240 bytes transferred in 34.731815 secs (309152234 bytes/sec) - 295MB/s > > With 2 parallel dd jobs : 345MB/s > With 4 parallel dd jobs : 502MB/s > > > > ### Questions : > > Why such a difference ? > Where are the 167MB/s (462-295) lost ? Network delays, I suppose. A single dd(1) would spend some time waiting for the data to get pushed over the network - due to delays (lag), not bandwidth. Having multiple ones makes it possible to compensate, by having multiple outstanding IO operations.