From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755229AbZECOV0 (ORCPT ); Sun, 3 May 2009 10:21:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752408AbZECOVR (ORCPT ); Sun, 3 May 2009 10:21:17 -0400 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:49344 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751717AbZECOVQ (ORCPT ); Sun, 3 May 2009 10:21:16 -0400 Subject: Re: [PATCH 00/16] DRBD: a block device for HA clusters From: James Bottomley To: david@lang.hm Cc: Willy Tarreau , Bart Van Assche , Andrew Morton , Philipp Reisner , linux-kernel@vger.kernel.org, Jens Axboe , Greg KH , Neil Brown , Sam Ravnborg , Dave Jones , Nikanth Karthikesan , Lars Marowsky-Bree , Kyle Moffett , Lars Ellenberg In-Reply-To: References: <1241090812-13516-1-git-send-email-philipp.reisner@linbit.com> <20090501015902.ed8b56d3.akpm@linux-foundation.org> <20090503053557.GH570@1wt.eu> Content-Type: text/plain Date: Sun, 03 May 2009 09:21:14 -0500 Message-Id: <1241360474.5596.4.camel@mulgrave.int.hansenpartnership.com> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 (2.22.3.1-1.fc9) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2009-05-02 at 22:40 -0700, david@lang.hm wrote: > On Sun, 3 May 2009, Willy Tarreau wrote: > > > On Sat, May 02, 2009 at 09:33:35AM +0200, Bart Van Assche wrote: > >> On Fri, May 1, 2009 at 10:59 AM, Andrew Morton > >> wrote: > >>> On Thu, 30 Apr 2009 13:26:36 +0200 Philipp Reisner wrote: > >>> > >>>> This is a repost of DRBD > >>> > >>> Is it being used anywhere for anything? If so, where and what? > >> > >> One popular application is to run iSCSI and HA software on top of DRBD > >> in order to build a highly available iSCSI storage target. > > > > Confirmed, I have several customers who're doing exactly that. > > I will also say that there are a lot of us out here who would have a use > for DRDB in our HA setups, but have held off implementing it specificly > because it's not yet in the upstream kernel. Actually, that's not a particularly strong reason because we already have an in-kernel replicator that has much of the functionality of drbd that you could use. The main reason for wanting drbd in kernel is that it has a *current* user base. Both the in kernel md/nbd and drbd do sync and async replication with primary side bitmaps. The main differences are: * md/nbd can do 1 to N replication, * drbd can do active/active replication (useful for cluster filesystems) * The chunk size of the md/nbd is tunable * With the updated nbd-tools, current md/nbd can do point in time rollback on transaction logged secondaries (a BCS requirement) * drbd manages the mirror state explicitly, md/nbd needs a user space helper And probably a few others I forget. James