From owner-freebsd-questions@FreeBSD.ORG Thu Sep 15 15:37:02 2011 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 72F17106564A for ; Thu, 15 Sep 2011 15:37:02 +0000 (UTC) (envelope-from juvix88@gmail.com) Received: from mail-qy0-f175.google.com (mail-qy0-f175.google.com [209.85.216.175]) by mx1.freebsd.org (Postfix) with ESMTP id 28EF98FC0C for ; Thu, 15 Sep 2011 15:37:02 +0000 (UTC) Received: by qyk10 with SMTP id 10so5475859qyk.13 for ; Thu, 15 Sep 2011 08:37:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=message-id:disposition-notification-to:date:from:user-agent :mime-version:to:cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=gKwo4nt6GyF+cyISUQjdY0kD+MKZmM4gNQ1z9QJPBk8=; b=YQIGNqE8vV3z/QFgOPSL1u41QPE+9VAdXlab9CfvtC8Q81Ip7Zk9yVXznkZ7H8APXy nO+SoC8BfgkbYfTAOFshSJGU3ldLdOvtqRujKgtawE/CIIXOtirmriEdYhaWGCxOXg0J 3qliJmg6iFuvZrMxX++nlFrC+hWK6oSarQ200= Received: by 10.224.202.72 with SMTP id fd8mr1127264qab.184.1316101021531; Thu, 15 Sep 2011 08:37:01 -0700 (PDT) Received: from [192.168.0.199] (ool-18ba4338.dyn.optonline.net. [24.186.67.56]) by mx.google.com with ESMTPS id cc12sm7757993qab.16.2011.09.15.08.37.00 (version=SSLv3 cipher=OTHER); Thu, 15 Sep 2011 08:37:00 -0700 (PDT) Message-ID: <4E721B9B.2020300@gmail.com> Date: Thu, 15 Sep 2011 11:36:59 -0400 From: Jonathan Vomacka User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0.2) Gecko/20110902 Thunderbird/6.0.2 MIME-Version: 1.0 To: Matthew Seaman References: <4E709F62.60705@gmail.com> <4E70B269.4020900@infracaninophile.co.uk> <4E70F79A.3090806@infracaninophile.co.uk> In-Reply-To: <4E70F79A.3090806@infracaninophile.co.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Michael Sierchio , freebsd-questions@freebsd.org Subject: Re: Recommended SWAP space for large amounts of ram (8GB) X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Sep 2011 15:37:02 -0000 Thanks Matthew / Michael for your responses on this. On 9/14/2011 2:51 PM, Matthew Seaman wrote: > On 14/09/2011 18:27, Michael Sierchio wrote: >> On Wed, Sep 14, 2011 at 6:55 AM, Matthew Seaman >> wrote: >> >>>> ... In these days of plentiful RAM, the new rule of thumb is "if you're >>>> swapping, then you're doing it wrong." > >> I think your response follows the excellent pedagogical principle: "a >> little inaccuracy saves a lot of explanation." But... disk is still >> (by far) the cheapest commodity, and the opportunistic paging >> algorithm manages VM very well. VM is not by any means obsolete, and >> seeing paging behavior is not a sign of a misconfigured system. > > Well, yes. I was certainly glossing over a lot of complexity -- but I > would maintain that I am fundamentally correct. > > Having some pages swapped out is absolutely not a problem. True. In > fact, it's a positive benefit: swapping out memory pages that are > exceedingly rarely referenced makes more room in RAM for more actively > used pages. > > On the other hand, having pages continually swapping in and out > definitely is a problem in terms of performance, given that disk IO > takes of the order of milliseconds, while reference to main RAM is of > the order of microseconds or less. Orders of magnitude faster. > > Now, while disk may well be the much the cheapest storage medium > available, that's only part of the expense. In fact, up-front capital > expenditure on the kit (perhaps several thousand pounds/euros/dollars) > is outweighed by the operational expense (power, cooling, hardware > support etc.) over the life of the equipment, so spending a bit more > (capex) on components that run at lower power (opex) makes a lot of > sense. Even more, if the server is being used for eg. e-Commerce, then > the volume of the transactions and the data processed by the server > makes all the difference to your margin: the more you can do with the > same hardware - viz, the more efficiently and faster you can make the > hardware run - then the more profit you make. Buying more RAM is > peanuts on that scale. > > Cheers, > > Matthew >