On 2016-06-25 19:58, Chris Murphy wrote:
>> Wow. So it sees the data strip corruption, uses good parity on disk to
>> fix it, writes the fix to disk, recomputes parity for some reason but
>> does it wrongly, and then overwrites good parity with bad parity?
> The wrong parity, is it valid for the data strips that includes the
> (intentionally) corrupt data?
> Can parity computation happen before the csum check? Where sometimes you get:
> read data strips > computer parity > check csum fails > read good
> parity from disk > fix up the bad data chunk > write wrong parity
> (based on wrong data)?
> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/fs/btrfs/raid56.c?id=refs/tags/v4.6.3
> 2371-2383 suggest that there's a parity check, it's not always being
> rewritten to disk if it's already correct. But it doesn't know it's
> not correct, it thinks it's wrong so writes out the wrongly computed
> parity?

The parity is not valid for both the corrected data and the corrupted data. It 
seems that the scrub process copy the contents of the disk2 to disk3. It could 
happens only if the contents of disk1 is zero.


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