Re: Raid recovery. Help wanted!

[Evgeny Koryanov <evgeny.koryanov@maris.no>]

On 21.04.2013 20:40, Mathias Burén wrote:
> On 21 April 2013 17:16, Evgeny Koryanov <evgeny.koryanov@maris.no> wrote:
>> Hello everybody!
>>
>> Yesterday I met a problem with one of raid5 arrays build by mdadm on three
>> (sd[bcd]) 1.5T devices.
>> I found array in degraded state with sdd fail. Drive becomes fail state
>> after power jump.
>> Server supplied by UPS but this seems was not good enough - server was not
>> rebooted but one drive as I said becomes fail state.
>> I simply reattaches it and array started rebuilding but fails after couple
>> of %'s passed with sdc becomes fail!!!
>> I assemble array again with sd[bc] and tried to attach sdd again: picture
>> repeated rebuild fails.
>> So I have sdb in sync state, sdc - failed and sdd spare. I checked SMARTs of
>> drives to understand reason of such behavior and
>> found it clean on all devices. Than I tried to dd if=/dev/sd[bcd]
>> of=/dev/null and found that dd also fails with IO error.
>> After dd bad blocks started appears in SMART :)
>> Finally I have:
>> sdb - sync
>> sdc - fail
>> sdd - spare
>> states and a number of bads on each hdd in random places...
>>
>> Could any one suggest how can I assemble this array now in read-only mode to
>> try to copy data?!
>> Theoretically data on sdd should not be rewritten and it still should be
>> possible to try recover data (meaning that bads appears in quite different
>> places)...
>> May be you know utility which helps recover data or the way how to start
>> array in read-only mode preventing becomes it to degraded state
>> and force md device to try recover data using readable places from each
>> devise???
>> Or any other ideas appreciated! Thanks, any way...
>>
>> Best regards,
>>                  Evgeny.
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> Hi,
>
> Could you post the smartctl -a output of all the drives? If 2 drives
> are failling you might want to derescue them somewhere and assemble
> the RAID from that.
>
> Mathias
Hi, Mathis.

Will post it tomorrow - it's down now and I'm not around.
But as per your suggestion: still not clear for me is it good idea - as 
soon as I will copy valid data to another drive
information about bad's places will be lost (for md device driver) and 
bad blocks physically will be replaced by zeros.
And what will happen after assembling and trying to read places where 
bad blocks was (where array marked sync and blocks are
not consistent - redundant part zeroed) - will md read properly? will md 
mark drive fail as soon as find async (zeroed) block ans start resync... 
Actually I did not found in mdadm read-only assembling mode which will 
prevent such behavior!

Best regards,
                     Evgeny.

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