From mboxrd@z Thu Jan 1 00:00:00 1970 From: Adam Goryachev Subject: Re: [RFE] Please, add optional RAID1 feature (= chunk checksums) to make it more robust Date: Fri, 27 Jul 2012 16:06:02 +1000 Message-ID: <50122FCA.3070304@websitemanagers.com.au> References: <500CD32E.4000800@hardwarefreak.com> <542194327.593466.1343036057599.JavaMail.root@redhat.com> <20120723170320.GA2691@lazy.lzy> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Linux RAID List-Id: linux-raid.ids On 24/07/12 07:31, Drew wrote: > Been mulling this problem over and I keep getting hung up on one > problem with ECC on a two disk RAID1 setup. > > In the event of silent corruption of one disk, which one is the good > copy? > > It works fine if the ECC code is identical across both mirrors. Just > checksum both chunks and discard the incorrect one. > > It also works fine if the ECC codes are corrupted but the data > chunks are identical. Discard the bad checksum. > > What if the corruption goes across several sectors and both data & > ECC chuncks are corrupted? Now you're back to square one. I know I'm a bit late to this discussion, and I know very little about the code level/etc... however, I thought the whole point of the checksum is to determine that the data + checksum do not match, therefore the data is wrong and should be discarded. You would re-write the data and checksum from another source (ie, the other drive in RAID1, or other drives in RAID5/6 etc...). ie, it should be treated the same as a bad block / non-readable sector (or lots of unreadable sectors....) Regards, Adam -- Adam Goryachev Website Managers www.websitemanagers.com.au