> So let's say you read a full RAID-5 stripe including parity and the parity does not match because of a silent error.
If you have an "iffy" sector that is on th eway out you might get a decent read after a few attempts. You can then make sure that the blocks on the other drives are OK and (assuming all the failures are in the same device) drop the problem device when done.
In reality most drives these days do this for you: a certain number of sectors are reserved for reallocation in the case of small surface failures so the drive itself will retry a few times to get a reliable read (each sector on a disk has checksums that allow error detection) then the controller will remap that sector. This happening once or twice is considered normal wear and tear, this heppening beyond a certain threshold or a certain rate is a sign of imminent failure and is measureed by SMART indicators - so running the scan will not let md raid do much directly but will give the drive chance to remap data that is in danger (and if you have mdadm setup right, email you a warning if you shoudl consider dropping the drive immediately and replace it).
If you have an "iffy" sector that is on th eway out you might get a decent read after a few attempts. You can then make sure that the blocks on the other drives are OK and (assuming all the failures are in the same device) drop the problem device when done.
In reality most drives these days do this for you: a certain number of sectors are reserved for reallocation in the case of small surface failures so the drive itself will retry a few times to get a reliable read (each sector on a disk has checksums that allow error detection) then the controller will remap that sector. This happening once or twice is considered normal wear and tear, this heppening beyond a certain threshold or a certain rate is a sign of imminent failure and is measureed by SMART indicators - so running the scan will not let md raid do much directly but will give the drive chance to remap data that is in danger (and if you have mdadm setup right, email you a warning if you shoudl consider dropping the drive immediately and replace it).