From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934667AbXGKWpa (ORCPT ); Wed, 11 Jul 2007 18:45:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762113AbXGKWpN (ORCPT ); Wed, 11 Jul 2007 18:45:13 -0400 Received: from mexforward.lss.emc.com ([128.222.32.20]:21961 "EHLO mexforward.lss.emc.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759683AbXGKWpK (ORCPT ); Wed, 11 Jul 2007 18:45:10 -0400 Message-ID: <46955D45.8010606@emc.com> Date: Wed, 11 Jul 2007 18:44:21 -0400 From: Ric Wheeler Reply-To: ric@emc.com User-Agent: Thunderbird 2.0.0.4 (Windows/20070604) MIME-Version: 1.0 To: Valdis.Kletnieks@vt.edu CC: Tejun Heo , 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 Subject: Re: [dm-devel] Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. 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> In-Reply-To: <4758.1184110800@turing-police.cc.vt.edu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-PMX-Version: 4.7.1.128075, Antispam-Engine: 2.5.1.298604, Antispam-Data: 2007.7.6.21134 X-PerlMx-Spam: Gauge=, SPAM=1%, Reasons='EMC_FROM_0+ -3, __CT 0, __CTE 0, __CT_TEXT_PLAIN 0, __HAS_MSGID 0, __MIME_TEXT_ONLY 0, __MIME_VERSION 0, __SANE_MSGID 0, __USER_AGENT 0' Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@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? > There are ways to query devices (think of hdparm -I in S-ATA/P-ATA drives, SCSI has similar queries) to see what kind of device you are talking to. I am not sure it is worth the trouble to do any automatic detection/handling of this. In this specific case, it is more a case of when you attach a high end (or mid-tier) device to a server, you should configure it without barriers for its exported LUNs. ric