From mboxrd@z Thu Jan 1 00:00:00 1970 From: Piergiorgio Sartor Subject: Re: mismatch_cnt again Date: Sun, 15 Nov 2009 22:05:42 +0100 Message-ID: <20091115210542.GA6826@lazy.lzy> References: <87tyx6tpcb.fsf@frosties.localdomain> <4AF58B20.3000409@redhat.com> <87iqdlaujb.fsf@frosties.localdomain> <4AF74B61.6000102@rabbit.us> <20091109185632.GA2723@lazy.lzy> <73ebdcee169f46611d411755f9aaca5b.squirrel@neil.brown.name> <20091109215443.GA4143@lazy.lzy> <20091110195222.GA2777@lazy.lzy> <19196.50782.113024.239657@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <19196.50782.113024.239657@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Piergiorgio Sartor , Peter Rabbitson , Goswin von Brederlow , Doug Ledford , Michael Evans , Eyal Lebedinsky , linux-raid list List-Id: linux-raid.ids Hi, > I think just "block ABC is inconsistent" is sufficient. > user-space can then quiesce that part of the array, read the relevant > blocks, do any analysis that might be appropriate, and report to the > admin. personally I think user space is good for this kind of operations. I think the point here is not if this kind of recovery should be in kernel space or not, but to have this kind of recovery. > That is a very interesting threat scenario - occasional bit flip on > read between media and memory. I had a drive like that once. One > particular bit in the sector would fairly often return '1' no matter > what had been written. I had it in a RAID1 and it quickly made a mess > of the filesystem. In my case, a further analisys showed that the "bits" where always *written* correctly, but the reading operation was, sometimes, flipping bits. This was especially nasty, because, without "resync" the array would have been always fine. > As you say, there is nothing that md can or should do about this > except report that something odd is happening, which it does, and > report where it is happening, which it does not. Well, md specifically may or may not have the infrastructure to use the RAID-6 parity to correct this sort of issues. Nevertheless, using the RAID-6 double parity, in user or kernel space, is really one point for software RAID. bye, -- piergiorgio