From owner-svn-src-all@FreeBSD.ORG Fri Dec 11 01:47:37 2009 Return-Path: Delivered-To: svn-src-all@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 55628106566B; Fri, 11 Dec 2009 01:47:37 +0000 (UTC) (envelope-from sobomax@FreeBSD.org) Received: from sippysoft.com (gk1.360sip.com [72.236.70.240]) by mx1.freebsd.org (Postfix) with ESMTP id 15EEE8FC14; Fri, 11 Dec 2009 01:47:36 +0000 (UTC) Received: from [192.168.1.38] (S0106005004e13421.vs.shawcable.net [70.71.167.197]) (authenticated bits=0) by sippysoft.com (8.14.3/8.14.3) with ESMTP id nBB1lYYd018094 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Thu, 10 Dec 2009 17:47:35 -0800 (PST) (envelope-from sobomax@FreeBSD.org) Message-ID: <4B21A4B9.3070005@FreeBSD.org> Date: Thu, 10 Dec 2009 17:47:37 -0800 From: Maxim Sobolev Organization: Sippy Software, Inc. User-Agent: Thunderbird 2.0.0.23 (Windows/20090812) MIME-Version: 1.0 To: Alexander Motin References: <200912102351.nBANpOKc078607@svn.freebsd.org> In-Reply-To: <200912102351.nBANpOKc078607@svn.freebsd.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: svn-src-stable@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, svn-src-stable-8@FreeBSD.org Subject: Re: svn: stable/8/sbin/geom/class/mirror X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 11 Dec 2009 01:47:37 -0000 Alexander Motin wrote: > Author: mav > Date: Thu Dec 10 23:51:24 2009 > New Revision: 200373 > URL: http://svn.freebsd.org/changeset/base/200373 > > Log: > MFC r200282, r200290: > Change gmirror default balance algorithm from "split" to improved "load". > "split" is very ineffective for devices with rotating media as HDDs. > To be effective, it needs that transfer time reduction due to block > splitting was bigger then access time increase due to non-sequential > access. For modern HDDs I was able to reproduce it only with read sizes > of 2MB and above, which is almost not applicable in real life. > "load" algorithm same time is more universal and effective now. The other problem with real hard drives is that they usually read much more data than requested. Some suggest that they read as much as one track each time the data is not in cache even if one sector has been requested, therefore splitting request of any reasonable size is meaningless, as it would simply cause both drives to load essentially the same data, wasting half of available I/O bandwidth and in addition you cause both heads to do seek, which makes it even worse. -Maxim