Goswin von Brederlow wrote:
Piergiorgio Sartor <piergiorgio.sartor@xxxxxxxx> writes:
On 11/07/2009 03:58 PM, Doug Ledford wrote:
[...]
I'm very quickly starting to become dubious of the current mismatch_cnt
implementation. I think a kernel patch is in order and I may just work
on that today. Here's the deal: a non-0 mismatch count is worthless if
you don't also tell people *where* the mismatch is so they can
investigate it and correct it.
You're perfectly right.
And this, again, fits in the discussion of RAID-6 error
check and, potentially, repair.
Ideally the log should tell which (RAID) address has a
mismatch and, in case of RAID-6, if a specific device
could be faulty at that position.
Actual in raid6 mode if one parity block is bad but the other is
correct I would expect that to automatically repair the bad block, at
least optionally. Same with a 3+ way mirror and one mirror being bad.
In general if a block is bad and the kernel can isolate which block in
a stripe is bad then it should repair it while checking.
While I agree totally on what the kernel *should* do, AFAIK it does no
such thing. In fact, I believe that even with a three way mirror the
mismatch is "fixed" by picking one copy at random and writing it over
the others, rather than voting.
I haven't looked at this in ages, but that's my memory. Like Dennis
Miller, "I could be wrong."
--
Bill Davidsen <davidsen@xxxxxxx>
"We can't solve today's problems by using the same thinking we
used in creating them." - Einstein
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