From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Rabbitson Subject: Re: mismatch_cnt questions - how about raid10? Date: Mon, 12 Mar 2007 15:26:49 +0100 Message-ID: <45F56329.4000407@rabbit.us> References: <17898.45673.573800.56474@notabene.brown> <17899.17901.429001.702653@notabene.brown> <45ED3CB1.8070003@rabbit.us> <17901.16476.282987.982971@notabene.brown> <45ED48DB.6030002@rabbit.us> <17908.59047.688420.79050@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17908.59047.688420.79050@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > On Tuesday March 6, rabbit@rabbit.us wrote: > > Though it is less likely, a regular filesystem could still (I think) > genuinely write different data to difference devices in a raid1/10. > > So relying on mismatch_cnt for early problem detection probably isn't > really workable. > > And I think that if a drive is returning bad data without signalling > an error, then you are very much into the 'late' side of problem > detection. I agree with the later, but my concern is not that much with the cause, but with the effect. From past discussion on the list I gather that no special effort is made to determine which chunk to take as 'valid', even though more than 2 logically identical chunks might be present (raid1/10). And you also seem to think that the DMA syndrome might even apply to plain fast-changing filesystems, left alone something with multiple layers (fs on lvm on raid). So here is my question: how (theoretically) safe it is to use a raid1/10 array for something very disk intensive, e.g. a mail spool? How likely it is that the effect you described above will creep different blocks onto disks, and subsequently will return the wrong data to the kernel? Should I look into raid5/6 for this kind of activity, in case both uptime and data integrity are my number one priorities, and I am willing to sacrifice performance? Thank you