On 05/08/2017 10:50 AM, Nix wrote: > I wonder... scrubbing is not very useful with md, particularly with RAID > 6, because it does no writes unless something mismatches, This is wrong. The purpose of scrubbing is to expose any sectors that have degraded (as Wol describes) to the point of generating a read error. A "check" scrub only writes back to the sectors that report a URE, giving the drive firmware a chance to fix or relocate the sector. A check scrub will NOT write on mismatch, just increment the mismatch counter. This is the recommended regular scrubbing operation. You want to know when mismatches occur. > If there was a way to get md to *rewrite* everything during scrub, > rather than just checking, this might help (in addition to letting the > drive refresh the magnetization of absolutely everything). This is actually counterproductive. Rewriting everything may refresh the magnetism on weakening sectors, but will also prevent the drive from *finding* weakening sectors that really do need relocation. Phil -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
