From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Kampe Subject: Re: ceph and efficient access of distributed resources Date: Mon, 15 Apr 2013 15:38:32 -0700 Message-ID: <516C8168.40402@inktank.com> References: <51683184.9010301@inktank.com> <516C7E55.1050801@inktank.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-pb0-f48.google.com ([209.85.160.48]:60897 "EHLO mail-pb0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932513Ab3DOWie (ORCPT ); Mon, 15 Apr 2013 18:38:34 -0400 Received: by mail-pb0-f48.google.com with SMTP id xb4so2739013pbc.21 for ; Mon, 15 Apr 2013 15:38:34 -0700 (PDT) In-Reply-To: <516C7E55.1050801@inktank.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Gandalf Corvotempesta Cc: Matthias Urlichs , "ceph-devel@vger.kernel.org" If I correctly understand the discussion, you are correct that I/O could be saved by doing this ... were it not for the fact the I/O in question is already being saved much more effectively by someone else. The entire web is richly festooned with cache servers whose sole raison d'etre is to solve precisely this problem. They are so good at it that back-bone providers often find it more cash-efficient to buy more cache servers than to lay more fiber. Cache servers don't merely save disk I/O, they catch these requests before they reach the server (or even the backbone). > On 04/15/2013 01:06 PM, Gandalf Corvotempesta wrote: >> >>> Currently reads always come from the primary OSD in the placement group >>> rather than a secondary even if the secondary is closer to the client. >>> >> >> In this way, only one OSD will be involved in reading an object, this >> will >> result in a bottleneck if multiple clients needs to access to the same >> file. >> >> For example, a 3KB CSS file served by a webserver to 400 users, will be >> read just from one OSD. 400 users directed to 1 OSD while (in case of >> replica 3) other 2 OSDs are available?