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

On Fri, 14 Sep 2012 09:16:20 +0200 (CEST) Mikael Abrahamsson
[off-list ref] wrote:

On Thu, 13 Sep 2012, Chris Murphy wrote:

quoted

"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.