Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753206AbYCQRUL (ORCPT ); Mon, 17 Mar 2008 13:20:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751445AbYCQRT6 (ORCPT ); Mon, 17 Mar 2008 13:19:58 -0400 Received: from mail.lang.hm ([64.81.33.126]:58163 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750762AbYCQRT6 (ORCPT ); Mon, 17 Mar 2008 13:19:58 -0400 Date: Mon, 17 Mar 2008 10:23:10 -0700 (PDT) From: david@lang.hm X-X-Sender: dlang@asgard.lang.hm To: Daniel Phillips cc: David Newall , Alan Cox , Willy Tarreau , linux-kernel@vger.kernel.org Subject: Re: [ANNOUNCE] Ramback: faster than a speeding bullet In-Reply-To: Message-ID: References: <200803092346.17556.phillips@phunq.net> <200803162252.58274.phillips@phunq.net> <200803170116.19546.phillips@phunq.net> User-Agent: Alpine 1.00 (DEB 882 2007-12-20) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1640 Lines: 37 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 never out of date.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) David Lang -- 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/