Re: Huge values of mismatch_cnt on RAID 6 arrays under Fedora 18

[Wolfgang Denk <wd@denx.de>]

Dear Chris Murphy,

In message <3DB28596-B1D6-48A9-9520-4CF9D367E39D@colorremedies.com> you wrote:
> 
> > After running a "repair" on the array, both "check" and "raid6test"
> > would not report any further issues.
> 
> Yes but this would be consistent with a derivative parity, written
> to disk and then checked against an algorithm that expects derivative
> parity. What happens if you go back to the old kernel before all the
> problems were happening and you do a check? What happens if you go
> back to a Fedora kernel you know exhibited the problem and you do a
> check?

I cannot test the exact old kernel I was running before any more;
Fedora has released an update in the meantime, and they do not keep
older updates around, only the very latest one - which is the same
version as causes the problems.  When using the (really old) kernel
from the installation media, I see the same behaviour as with current
mainline: I have to run a "repair", and then the array is, and
remains, clean.

With the current Fedora kernel, the first check will report errors
which do not go away permanently, not even with a "repair".

> Question for Piergiorgio is if check and raid6test use the same, or
> independent, code for checking parity?

My impression is that they must use different code - raid6test takes
much, much longer and causes a much higher CPU load than running
"check".

> I think a bug needs to be filed with the information you have thus far.

I did this, actually in parallel with reporting the issues here:
https://bugzilla.redhat.com/show_bug.cgi?id=904831

I think the relevant Fedora people are on Cc:, but there was zero
response so far; seems potential data loss is of no concern to the
Fedora project :-(

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de
You don't have to worry about me. I might have been born yesterday...
but I stayed up all night.