[Durham] SMART errors

Oliver Burnett-Hall olly at burnett-hall.co.uk
Sun Nov 9 15:33:36 UTC 2014


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Does anyone know much about SMART?

I've got my backups going to a system which is running a three-disk
RAID5 array. For the last few days I've been receiving warnings from
smartd about problems with one of the disks and from mdadm about a
degraded array. I'm a bit clueless about all of this and Google hasn't
given my any idiot-friendly primers for what's happening.

First off, the SMART errors. I'm getting these two messages from smartd
repeated in syslog every half hour:
    Device: /dev/sdb [SAT], 14 Currently unreadable (pending) sectors
    Device: /dev/sdb [SAT], 14 Offline uncorrectable sectors

That seems a fairly clear: /dev/sdb is failing. However when I run any
self-tests (both short and long) the drive passes them. Surely that
can't be right?

The messages from mdadm are even less helpful. It says:
    A DegradedArray event had been detected on md device /dev/md0.
    Faithfully yours, etc.
    P.S. The /proc/mdstat file currently contains the following:
    Personalities : [raid1]
    md0 : active raid1 sdc1[1]
        1953279872 blocks super 1.2 [2/1] [_U]
    unused devices: <none>

That is confusing me. I set up a RAID5 array across sdb, sdc and sdd
but now it's talking about a RAID1 only on sdc. If sdb has died should
it not still being showing a degraded RAID5 on sdc and sdd

The drive is still well within its warranty period so there's the
obvious solution of getting a replacement drive off WD, but I'm curious
to understand what's happening here.

- - olly

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