From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: Why does one get mismatches? Date: Thu, 25 Feb 2010 08:47:59 +0000 Message-ID: <4B86393F.4040707@anonymous.org.uk> References: <869541.92104.qm@web51304.mail.re2.yahoo.com> <4B67451F.8040206@tmr.com> <20100202093738.44b4fece@notabene.brown> <4B684087.50001@tmr.com> <20100211161444.7a0ea7bb@notabene.brown> <20100211175133.GA30187@atlantis.cc.ndsu.nodak.edu> <4B7B0D45.7040801@tmr.com> <6db64f7872286165ac1fd3436e9d6476@localhost> <20100218100547.7aecdc34@notabene.brown> <4B853BBF.7000607@tmr.com> <20100225083203.4936ee63@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100225083203.4936ee63@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 24/02/2010 21:32, Neil Brown wrote: [...] > If you open /dev/md0 with O_DIRECT there is no page cache involved and so no > setting of Dirty flags. So you could engineer a situation with O_DIRECT > that writes different data to the two devices, but you would have to try > fairly hard. Hang on. O_DIRECT sets off all sort of alarm bells for me, not that I understand it properly. Of course there's O_DIRECT on files too. Linus Torvalds is quite outspoken about it: http://kerneltrap.org/node/7563 Could we be seeing mismatches because applications are opening their files with O_DIRECT in a (perhaps misguided) attempt to get better performance? Cheers, John.