Re: Suggestion needed for fixing RAID6

[MRK <mrk@shiftmail.org>]

On 05/03/2010 12:04 PM, MRK wrote:
> On 05/03/2010 04:17 AM, Neil Brown wrote:
>> On Sat, 1 May 2010 23:44:04 +0200
>> "Janos Haar"<janos.haar@netcenter.hu>  wrote:
>>
>>> The general problem is, i have one single-degraded RAID6 + 2 
>>> badblock disk
>>> inside wich have bads in different location.
>>> The big question is how to keep the integrity or how to do the 
>>> rebuild by 2
>>> step instead of one continous?
>> Once you have the fix that has already been discussed in this thread, 
>> the
>> only other problem I can see with this situation is if attempts to 
>> write good
>> data over the read-errors results in a write-error which causes the 
>> device to
>> be evicted from the array.
>>
>> And I think you have reported getting write
>> errors.
>
> His dmesg AFAIR has never reported any error of the kind "raid5:%s: 
> read error NOT corrected!! " (the error message you get on failed 
> rewrite AFAIU)
> Up to now (after my patch) he only tried with MD above DM-COW and DM 
> was dropping the drive on read error so I think MD didn't get any 
> opportunity to rewrite.
>
> It is not clear to me what kind of error MD got from DM:
>
> Apr 29 09:50:29 Clarus-gl2k10-2 kernel: device-mapper: snapshots: 
> Invalidating snapshot: Error reading/writing.
> Apr 29 09:50:29 Clarus-gl2k10-2 kernel: ata8: EH complete
> Apr 29 09:50:29 Clarus-gl2k10-2 kernel: raid5: Disk failure on dm-1, 
> disabling device.
>
> I don't understand from what place the md_error() is called...
> [CUT]

Oh and there is another issue I wanted to expose:

His last dmesg:
http://download.netcenter.hu/bughunt/20100430/messages

Much after the line:
Apr 29 09:50:29 Clarus-gl2k10-2 kernel: raid5: Disk failure on dm-1, 
disabling device.

there are many lines like this:
Apr 29 09:50:29 Clarus-gl2k10-2 kernel: raid5:md3: read error not 
correctable (sector 1662189872 on dm-1).

How come MD still wants to read from a device it has disabled?
looks like a problem to me...
MD also scrubs failed devices during check?