linux-kernel - [raid] How does raid-check know which piece of data is the correct one

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Message-ID: <20160819154846.2ad3f35a@ulgy_thing>
Date:   Fri, 19 Aug 2016 15:48:46 -0400
From:   David Niklas <Hgntkwis@...mail.net>
To:     linux-kernel@...r.kernel.org
Subject: [raid] How does raid-check know which piece of data is the correct
 one

Hello,
please CC.
I switched to a RAID 5 array about a year ago and I run raid-check every
week, the problem is that I've gotten some corruption of some of my files
over time (HW failure and cable creep have caused the array to need to
rebuild a few times), and I wanted to try to figure it out if this was a
"before I switched to raid problem", or if there may be insufficient
protection from my raid array.
Here is the case where I'm uncertain. If I've got two bytes.
10101010 01010101 then they are probably xor'ed for parity and that would
make it 11111111. Ok, but if one or the other byte or the parity byte are
damaged how does raid-check rectify the problem? How does it know which
one is damaged.

Thanks,
David

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