Re: md raid behavior, bad sector uncorrectable read error

[Oliver Schinagl <oliver+list@schinagl.nl>]

On 08/19/12 11:47, Mikael Abrahamsson wrote:
> On Sat, 18 Aug 2012, Chris Murphy wrote:
>
>> If the affected chunk is rebuilt from parity (or copy in case of
>> mirror), does md raid issue a write command to write the rebuilt chunk
>> back to the disk at the same LBAs? If so, shouldn't this force the
>> drive to determine if the sector error is transient or persistent, and
>> if persistent the disk firmware will remap the bad sector to a reserve
>> sector?
>
> If I remember correctly from what has been described here before, a read
> error will cause a re-write with information created from parity, and
> the drive should figure it out (either is successfully writes the new
> information to the existing sector, or if it can't, it writes it to a
> spare sector (re-map)). If it throws a write error, the drive is kicked
> from the array (because a drive with write errors is clearly defective).
>
> So yes, you're correct in your assumption from what I know.
>
Also, SMARTd would throw up errors when monitoring such drive when a 
re-map occurs, mdadm may not even notice this if the remap happens 
successfully.