From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [dm-devel] Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. Date: Wed, 11 Jul 2007 11:49:57 +0900 Message-ID: <46944555.80509@gmail.com> References: <18006.38689.818186.221707@notabene.brown> <18010.12472.209452.148229@notabene.brown> <20070528094358.GM25091@agk.fab.redhat.com> <5201e28f0705290225v14fdac44hb0382a4137a84d01@mail.gmail.com> <20070529220500.GA6513@agk.fab.redhat.com> <5201e28f0705300212g3be16464u5ee1a4c80db27a11@mail.gmail.com> <465DAC72.1010201@cfl.rr.com> <5201e28f0705310414u1a9aebc4je135748274543946@mail.gmail.com> <465F9197.7060002@gmail.com> <465FC7B1.3060309@gmail.com> <4693D26D.2060004@emc.com> <4758.1184110800@turing-police.cc.vt.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: ric@emc.com, david@lang.hm, Stefan Bader , Phillip Susi , device-mapper development , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Jens Axboe , David Chinner , Andreas Dilger To: Valdis.Kletnieks@vt.edu Return-path: Received: from wa-out-1112.google.com ([209.85.146.176]:36336 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753100AbXGKCv2 (ORCPT ); Tue, 10 Jul 2007 22:51:28 -0400 Received: by wa-out-1112.google.com with SMTP id v27so2129663wah for ; Tue, 10 Jul 2007 19:51:27 -0700 (PDT) In-Reply-To: <4758.1184110800@turing-police.cc.vt.edu> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Valdis.Kletnieks@vt.edu wrote: > On Tue, 10 Jul 2007 14:39:41 EDT, Ric Wheeler said: > >> All of the high end arrays have non-volatile cache (read, on power loss, it is a >> promise that it will get all of your data out to permanent storage). You don't >> need to ask this kind of array to drain the cache. In fact, it might just ignore >> you if you send it that kind of request ;-) > > OK, I'll bite - how does the kernel know whether the other end of that > fiberchannel cable is attached to a DMX-3 or to some no-name product that > may not have the same assurances? Is there a "I'm a high-end array" bit > in the sense data that I'm unaware of? Well, the array just has to tell the kernel that it doesn't to write back caching. The kernel automatically selects ORDERED_DRAIN in such case. -- tejun