Re: raid1 issue after disk failure: both disks of the array are still active

[NeilBrown <neilb@suse.de>]

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On Fri, 14 Sep 2012 09:16:20 +0200 (CEST) Mikael Abrahamsson
<swmike@swm.pp.se> wrote:

> On Thu, 13 Sep 2012, Chris Murphy wrote:
> 
> > "check" records errors, no action is taken by the md driver to correct 
> > it, although the disk firmware itself may try reallocation. So far, that 
> > appears to not be the case.
> >
> > "repair" causes the md driver to write correct data (from copy or 
> > reconstructed from parity), which should force the disk firmware to 
> > reallocate the affected LBAs from bad physical sectors to good ones.
> >
> > It seems in this case "repair" is indicated.
> 
> I was under the impression that "check" would check if all data blocks and 
> parity are correct, and record if there is a parity mismatch. This would 
> then be corrected by using "repair" at a later time.
> 
> I was also under the impression that if there was a read error on a drive 
> during "check", that read error would be corrected using parity because 
> it's obviously a hard error, not a logical error.

Both of your impressions are correct.

NeilBrown

> 
> Could you (or someone else) please confirm that my impression is wrong and 
> if there indeed is a hard read error using "check", this will not be 
> corrected? I would be interested in knowing why this decision was taken to 
> have this behaviour, as I feel that if there is a hard read error, this 
> should always be corrected using parity.
> 


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