From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc MERLIN Subject: Re: How to force rewrite of a smart detected bad block with raid5: checkarray? Date: Wed, 19 Jan 2011 12:57:39 -0800 Message-ID: <20110119205739.GI7117@merlins.org> References: <4D372F1C.7080703@clear.net.nz> <20110119184914.GA27358@merlins.org> <20110120070133.47eccd10@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20110120070133.47eccd10@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Richard Scobie , Linux RAID Mailing List List-Id: linux-raid.ids On Thu, Jan 20, 2011 at 07:01:33AM +1100, NeilBrown wrote: > > > The kernel source, Documentation/md.txt. > > > > Ah, yes of course. Didn't think about looking there, thanks. > > "man md" is also an appropriate place to look. Ah yes. Thanks for that too. > > Mmmh, so I was curious as to how repair, when reading all the blocks of a > > stripe with no read errors, and finding a parity mismatch, would know which > > block was corrupted and needs to be rewritten. > > It doesn't repair the data - that would be impossible. It repairs the that's what I thought. > redundancy information which is all that raid really knows about. > i.e. if it finds an inconsistency it re-writes the parity block. Right, so it has only chance out of n to fix the right drive. Better than nothing though. > It isn't often useful. But if you parity blocks are wrong somehow, then it > can be useful. It will not recover data that you have already lost, but it > could make it less likely to lose more data. Fair enough. > md currently treats RAID6 just the same way as RAID5 - parity is re-written. > It is possible that more could be done, but it isn't completely clear that it > should - and it certainly isn't high on my priority list. Understood. So, I went back and read man md, and md.txt in the kernel Documentation tree, but I could not find documentation on this: echo 3907029168 > sync_min echo 3907029170 > sync_max and as per my other post, it didn't work for me on 2.6.36 (echo: write error: Invalid argument) Any suggestions? Thanks, Marc -- "A mouse is a device used to point at the xterm you want to type in" - A.S.R. Microsoft is to operating systems & security .... .... what McDonalds is to gourmet cooking Home page: http://marc.merlins.org/