Re: emergency call for help: raid5 fallen apart

["Stefan /*St0fF*/ Hübner" <stefan.huebner@stud.tu-ilmenau.de>]

Sorry @all, I had a few typos:

Stefan /*St0fF*/ Hübner schrieb:
> [...]
> BUT: if the drive takes let's say 2 min for internal error recovery to
> succeed of fail (whichever, doesn't matter), then the SG EH layer of the

-> succeed OR fail

> kernel will drop the disk, not md.  This forces md to drop the disk,
> also.  The conclusion is: a technology is needed to prevent another
> kernel level from dropping the disk.  This technology exists, it's
> called SCT-ERC (Smart Control Transport - Error Recovery Control).  It's
> the same as WD's TLER or Samsung's CCTL.  But it is non-volatile.  After

-> But it is volatile.

> a power on reset the timeout-values are reset to factory defaults.  So
> it needs to be set right before adding a disk to an array.
> (for more info: check www.t13.org, find the ATA8-ACS documents)
>> I do think we urgently need the hot reconstruction/recovery feature, so
>> failing drives can be recovered to fresh drives with two sources of
>> data, i.e. both the failing drive and the remaining drives in the array,
>> giving us two chances of recovering every sector.
> 
> I do not think this is easily possible.  One would have to keep a map
> about the "in sync" sectors of an array member and the "failed" sectors.
>  My guess is: this would need a partial redesign (again a new superblock
> type containing information about "failed segments" probably).
> Please correct me if I'm wrong and that is already included in 1.X (I'm
> mostly working on 0.90 Superblocks).
>> Cheers,
>>
>> John.
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> 
> Cheers,
> Stefan.
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