From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Clements Subject: Re: [PATCH 1/2] md bitmap bug fixes Date: Fri, 18 Mar 2005 12:03:43 -0500 Message-ID: <423B09EF.8070708@steeleye.com> References: <422F7621.8090602@steeleye.com> <16949.5768.392061.95882@cse.unsw.edu.au> <20050314094454.GK3858@marowsky-bree.de> <16949.26113.68948.938529@cse.unsw.edu.au> <20050314112403.GT3858@marowsky-bree.de> <16950.5692.594941.130741@cse.unsw.edu.au> <20050318103326.GA18819@marowsky-bree.de> <6ivqg2-qsn.ln1@news.it.uc3m.es> <20050318134255.GS18819@marowsky-bree.de> <7e6rg2-pj1.ln1@news.it.uc3m.es> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit In-Reply-To: <7e6rg2-pj1.ln1@news.it.uc3m.es> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Peter T. Breuer wrote: > Lars Marowsky-Bree wrote: > >>On 2005-03-18T13:52:54, "Peter T. Breuer" wrote: >>The problem is for multi-nodes, both sides have their own bitmap. When a >>split scenario occurs, > Here I think you mean that both nodes go their independent ways, due to > somebody tripping over the network cables, or whatever. Yes, or just a failover, where the active system crashes or is taken down (while the bitmap is dirty). >>and both sides begin modifying the data, that >>bitmap needs to be merged before resync, or else we risk 'forgetting' >>that one side dirtied a block. Right. And eventually we'd like to have that capability (of recombining bitmaps). > Could you set out the scenario very exactly, please, for those of us at > the back of the class :-). I simply don't see it. I'm not saying it's > not there to be seen, but that I have been unable to build a mental > image of the situation from the description :(. Typically, in a cluster environment, you set up a raid1 with a local disk and an nbd (or one of its variants) below it: [raid1] / \ [disk] [nbd] ---------> other system The situation he's talking about is, as you put it "somebody tripping over the network cables". In that case, you'll end up with this: system A system B [raid1] [raid1] / \ / \ [disk] [XXX] [disk] [XXX] Where there's a degraded raid1 writing only to the local disk on each system (and a dirty bitmap on both sides). The solution is to combine the bitmaps and resync in one direction or the other. Otherwise, you've got to do a full resync... -- Paul