On 13 November 2016 at 22:18, Anthony Youngman <antlists@xxxxxxxxxxxxxxx> wrote: > Quick first response ... > > On 13/11/16 18:46, Bruce Merry wrote: >> >> Hi >> >> I'm running software RAID1 across two drives in my home machine (LVM >> on LUKS on RAID1). I've just installed smartmontools and run short >> tests, and promptly received emails to tell me that one of the drives >> has 4 offline uncorrectable sectors and 3 current pending sectors. >> I've attached smartctl --xall output for sda (good) and sdb (bad). >> >> These drives are pretty old (over 5 years) so I'm going to replace >> them as soon as I have time (and yes, I have backups), but in the >> meantime I'd like advice on: >> > What drives are they? I'm guessing they're hunky-dory, but they don't fall > foul of timeout mismatch, do they? > > https://raid.wiki.kernel.org/index.php/Timeout_Mismatch smartctl reports "SCT Error Recovery Control command not supported". Does that mean I should be worried? Is there any way to tell whether a given drive I can buy online supports it? >> 1. What exactly this means. My understanding is that some data has >> been lost (or may have been lost) on the drive, but the drive still >> has spare sectors to remap things once the failed sectors are written >> to. Is that correct? > > > It may also mean that the four sectors at least, have already been remapped > ... I'll let the experts confirm. The three pending errors might be where a > read has failed but there's not yet been a re-write - and you won't have > noticed because the raid dealt with it. I'm guessing nothing has been remapped yet, because the Reallocated_Sector_Ct and Reallocator_Event_ct are both zero. >> 3. Assuming my understanding is correct, and that the sector falls >> within the RAID1 partition on the drive, is there some way I can >> recover the sectors from the other drive in the RAID1? As a last >> resort I imagine I could wipe the suspect drive and then rebuild it >> from the good one, but I'm hoping there's something less risky I can >> do. > > > Do a scrub? You've got seven errors total, which some people will say "panic > on the first error" and others will say "so what, the odd error every now > and then is nothing to worry about". The point of a scrub is it will > background-scan the entire array, and if it can't read anything, it will > re-calculate and re-write it. Yes, that sounds like what I need. Thanks to Google I found /usr/share/mdadm/checkarray to trigger this. It still has a few hours to go, but now the bad drive has pending sectors == 65535 (which is suspiciously power-of-two and I assume means it's actually higher and is being clamped), and /sys/block/md0/md/mismatch_cnt is currently at 1408. If scrubbing is supposed to rewrite on failed reads I would have expected pending sectors to go down rather than up, so I'm not sure what's happening. Thanks Bruce -- Dr Bruce Merry bmerry <@> gmail <.> com http://www.brucemerry.org.za/ http://blog.brucemerry.org.za/ -- 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
