hey Neil... i've been wanting to test out the reconstruct-on-read-error code... and i've had two chances to do so, but haven't be able to force md to read the appropriate block to trigger the code. i had two disks with SMART Current_Pending_Sector > 0 (which indicates pending read error) and i did SMART long self-tests to find out where the bad block was (it should show the LBA in the SMART error log)... one disk was in a raid1 -- and so it was kind of random which of the two disks would be read from if i tried to seek to that LBA and read... in theory with O_DIRECT i should have been able to randomly get the right disk, but that seems a bit clunky. unfortunately i didn't think of the O_DIRECT trick until after i'd given up and decided to just resync the whole disk proactively. the other disk was in a raid5 ... 5 disk raid5, so 20% chance of the bad block being in parity. i copied the kernel code to be sure, and sure enough the bad block was in parity... just bad luck :) so i can't force a read there any way that i know of... anyhow this made me wonder if there's some other existing trick to force such reads/reconstructions to occur... or perhaps this might be a useful future feature. on the raid5 disk i actually tried reading the LBA directly from the component device and it didn't trigger the read error, so now i'm a bit skeptical of the SMART log and/or my computation of the seek offset in the partition... but the above question is still interesting. -dean - 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
