From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752473AbXLDJPv (ORCPT ); Tue, 4 Dec 2007 04:15:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751107AbXLDJPn (ORCPT ); Tue, 4 Dec 2007 04:15:43 -0500 Received: from brick.kernel.dk ([87.55.233.238]:22516 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750862AbXLDJPn (ORCPT ); Tue, 4 Dec 2007 04:15:43 -0500 Date: Tue, 4 Dec 2007 10:13:34 +0100 From: Jens Axboe To: Neil Brown Cc: linux-kernel@vger.kernel.org Subject: Re: Is BIO_RW_FAILFAST really usable? Message-ID: <20071204091334.GG23294@kernel.dk> References: <18260.49019.684445.303719@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <18260.49019.684445.303719@notabene.brown> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 04 2007, Neil Brown wrote: > > I've been looking at use BIO_RW_FAILFAST in md/raid to improve > handling of some error cases. > > This is particularly significant for the DASD driver (s390 specific). > I believe it uses optic fibre to connect to the drives. When one of > these paths is unplugged, IO requests will block until an operator > runs a command to reset the card (or until it is plugged back in). > The only way to avoid this blockage is to use BIO_RW_FAILFAST. So > we really need BIO_RW_FAILFAST for a reliable RAID1 configuration on > DASD drives. > > However, I just tested BIO_RW_FAILFAST on my SATA drives: controller > > 02:06.0 RAID bus controller: Silicon Image, Inc. SiI 3114 [SATALink/SATARaid] Serial ATA Controller (rev 02) > > (not using the cards minimal RAID functionality) and requests fail > immediately and always with e.g. > > sd 2:0:0:0: [sdc] Result: hostbyte=DID_NO_CONNECT driverbyte=DRIVER_OK,SUGGEST_OK > end_request: I/O error, dev sdc, sector 2048 > > So fail fast obviously isn't generally usable. > > What is the answer here? Is the Silicon Image driver doing the wrong > thing, or is DASD doing the wrong thing, or is BIO_RW_FAILFAST > under-specified and we really need multiple flags or what? Hrmpf. It looks like the SCSI layer is a little too trigger happy. Any chance you could try and trace where this happens? -- Jens Axboe