Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755454AbYCQRdB (ORCPT ); Mon, 17 Mar 2008 13:33:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752593AbYCQRcy (ORCPT ); Mon, 17 Mar 2008 13:32:54 -0400 Received: from 1wt.eu ([62.212.114.60]:2510 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752577AbYCQRcx (ORCPT ); Mon, 17 Mar 2008 13:32:53 -0400 Date: Mon, 17 Mar 2008 18:30:01 +0100 From: Willy Tarreau To: david@lang.hm Cc: Daniel Phillips , David Newall , Alan Cox , linux-kernel@vger.kernel.org Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet Message-ID: <20080317173001.GD18229@1wt.eu> References: <200803092346.17556.phillips@phunq.net> <200803162252.58274.phillips@phunq.net> <200803170116.19546.phillips@phunq.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1822 Lines: 43 On Mon, Mar 17, 2008 at 10:23:10AM -0700, david@lang.hm wrote: > On Mon, 17 Mar 2008, david@lang.hm wrote: > > >On Mon, 17 Mar 2008, 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never out of date.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. > >> > >>>a local disk array has more write bandwidth than a network connection to > >>>a > >>>remote machine, so if you can mirror to a remote machine you can mirror > >>>to > >>>a local disk array. > >> > >>So you could potentially connect to a _huge_ disk array and write deltas > >>to it. The disk array would have to support roughly 3 Gbytes/second of > >>write bandwidth to keep up with the Violin ramdisk. Doable, but you are > >>now in the serious heavy iron zone. > > > >your network will do less then 1 Gbit/sec, so to mirror in real-time (what > >you claim is trivial) you would need at least 24 network connections in > >parallel. that's a LOT harder to setup then a high performance disk array. > > by the way, the only way to get this much bandwideth between two machines > is to directly connect PCI-e/16 card slots togeather. this is definantly > not commodity hardware anymore (if it's even possible, PCI-e has some very > short distance limitations) You can do that with 3 10GE NICS, though in practise that's not easy. Willy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/