Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261443AbVE2VQT (ORCPT ); Sun, 29 May 2005 17:16:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261444AbVE2VQS (ORCPT ); Sun, 29 May 2005 17:16:18 -0400 Received: from mail.gmx.net ([213.165.64.20]:35225 "HELO mail.gmx.net") by vger.kernel.org with SMTP id S261443AbVE2VQR (ORCPT ); Sun, 29 May 2005 17:16:17 -0400 X-Authenticated: #428038 Date: Sun, 29 May 2005 23:16:10 +0200 From: Matthias Andree To: Greg Stark Cc: Alan Cox , Matthias Andree , Arjan van de Ven , Linux Kernel Mailing List Subject: Re: Linux does not care for data integrity (was: Disk write cache) Message-ID: <20050529211610.GA2105@merlin.emma.line.org> Mail-Followup-To: Greg Stark , Alan Cox , Arjan van de Ven , Linux Kernel Mailing List References: <20050515152956.GA25143@havoc.gtf.org> <20050516.012740.93615022.okuyamak@dd.iij4u.or.jp> <42877C1B.2030008@pobox.com> <20050516110203.GA13387@merlin.emma.line.org> <1116241957.6274.36.camel@laptopd505.fenrus.org> <20050516112956.GC13387@merlin.emma.line.org> <1116252157.6274.41.camel@laptopd505.fenrus.org> <20050516144831.GA949@merlin.emma.line.org> <1116256005.21388.55.camel@localhost.localdomain> <87zmudycd1.fsf@stark.xeocode.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87zmudycd1.fsf@stark.xeocode.com> X-PGP-Key: http://home.pages.de/~mandree/keys/GPGKEY.asc User-Agent: Mutt/1.5.9i X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1305 Lines: 29 On Sun, 29 May 2005, Greg Stark wrote: > Oracle, Sybase, Postgres, other databases have hard requirements. They > guarantee that when they acknowledge a transaction commit the data has been > written to non-volatile media and will be recoverable even in the face of a > routine power loss. > > They meet this requirement just fine on SCSI drives (where write caching > generally ships disabled) and on any OS where fsync issues a cache flush. If I don't know what facts "generally ships disabled" is based on, all of the more recent SCSI drives (non SCA type though) I acquired came with write cache enabled and some also with queue algorithm modifier set to 1. > Worse, if the disk flushes the data to disk out of order it's quite > likely the entire database will be corrupted on any simple power > outage. I'm not clear whether that's the case for any common drives. It's a matter of enforcing write order. In how far such ordering constraints are propagated by file systems, VFS layer, down to the hardware, is the grand question. -- Matthias Andree - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/