From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754886AbYCQNz2 (ORCPT ); Mon, 17 Mar 2008 09:55:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753217AbYCQNzM (ORCPT ); Mon, 17 Mar 2008 09:55:12 -0400 Received: from mexforward.lss.emc.com ([128.222.32.20]:13690 "EHLO mexforward.lss.emc.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751946AbYCQNzL (ORCPT ); Mon, 17 Mar 2008 09:55:11 -0400 Message-ID: <47DE7780.2000505@emc.com> Date: Mon, 17 Mar 2008 09:52:00 -0400 From: Ric Wheeler Reply-To: ric@emc.com User-Agent: Thunderbird 2.0.0.9 (X11/20071031) MIME-Version: 1.0 To: Daniel Phillips CC: david@lang.hm, David Newall , Alan Cox , Willy Tarreau , linux-kernel@vger.kernel.org Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet References: <200803092346.17556.phillips@phunq.net> <200803162252.58274.phillips@phunq.net> <200803170116.19546.phillips@phunq.net> In-Reply-To: <200803170116.19546.phillips@phunq.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-PMX-Version: 4.7.1.128075, Antispam-Engine: 2.5.1.298604, Antispam-Data: 2007.8.30.53115 X-PerlMx-Spam: Gauge=, SPAM=1%, Reason='EMC_FROM_0+ -3, __CT 0, __CTE 0, __CT_TEXT_PLAIN 0, __HAS_MSGID 0, __MIME_TEXT_ONLY 0, __MIME_VERSION 0, __SANE_MSGID 0, __USER_AGENT 0' X-Tablus-Inspected: yes X-Tablus-Classifications: public X-Tablus-Action: allow Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Daniel Phillips wrote: > On Sunday 16 March 2008 23:49, david@lang.hm wrote: >>> Mirroring on the other hand, makes a realtime copy of a volume, that is >>> never out of date. >> so just mirror to a local disk array then. > > Great idea. Except that the disk array has millisecond level latency, > when what we trying to achieve is microsecond level latency. Just a point of information, most of the mid-tier and above disk arrays can do replication/mirroring behind the scene (i.e., you write to one array and it takes care of replicating your write to one or more other arrays). This behind the scene replication can be over various types of connections - IP or fibre channel probably are the two most common paths. That will still leave you with the normal latency for a small write to an array which is (when you hit cache) order of 1-2 ms... ric