From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [dm-devel] Re: Is there a grand plan for FC failover? Date: Sat, 31 Jan 2004 18:42:01 +0100 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20040131174201.GC11683@suse.de> References: <1075131446.2290.29.camel@mulgrave> <20040128100236.D11527@vienna.EGENERA.COM> <1075309052.2254.6.camel@mulgrave> <20040128130040.E11527@vienna.EGENERA.COM> <20040128124756.A7232@beaverton.ibm.com> <1075328066.2534.10.camel@mulgrave> <20040128165534.A9202@beaverton.ibm.com> <20040130194826.GC31596@reti> <20040131093037.GR11683@suse.de> <20040131115903.A4881@vienna.EGENERA.COM> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from ns.virtualhost.dk ([195.184.98.160]:30133 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S264963AbUAaRmN (ORCPT ); Sat, 31 Jan 2004 12:42:13 -0500 Content-Disposition: inline In-Reply-To: <20040131115903.A4881@vienna.EGENERA.COM> List-Id: linux-scsi@vger.kernel.org To: "Philip R. Auld" Cc: Joe Thornber , dm-devel@sistina.com, James Bottomley , Simon Kelley , SCSI Mailing List On Sat, Jan 31 2004, Philip R. Auld wrote: > Rumor has it that on Sat, Jan 31, 2004 at 10:30:37AM +0100 Jens Axboe said: > > On Fri, Jan 30 2004, Joe Thornber wrote: > > > It would be great to get some benchmarks to back up these arguments. > > > eg, performance of dm mpath with a simple round robin selector, > > > compared to a scsi layer implementation. Lifting the elevator (or > > > lowering dm) is a big piece of work that I wont even consider unless > > > there is very good reason; the reason probably needs to be broader > > > than just multipath too. Even if we did decide to do this, it won't > > > happen in 2.6. > > > > I suspect the problem really isn't that huge in 2.6, since most > > performance file systems are using mpage or building their own big > > bio's. So in a sense, some of the merging already does happen above dm > > (and the io scheduler). > > Out of curiosity, where does raw io fit into that in 2.6? raw io (or O_DIRECT io, same path) should work even better, always send out bio's as big as the underlying device can support. -- Jens Axboe