Re: mismatch_cnt again

Goswin von Brederlow
2009-11-08T15:32:58Z

Piergiorgio Sartor <piergiorgio.sartor@nexgo.de> 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.

> This would be already quite a huge step forward in improving
> the overall reliability of the RAID sub-system.
>
> Side note: in F11 there is this cron.weekly raid-check, but
> nothing is reported (per email to root) in case of mismatch.
> Is there any plan to add a such a facility?

In Debian it is monthly, first sunday of the month. Takes too long to
do weekly imho.

> Thanks.
>
> bye,

MfG
Goswin