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Re: ZFS RAIDZ2 and wd uncorrectable data error - why does ZFS not notice the hardware error?

Mr Roooster <> writes:

> The wd driver is retrying, (IIRC it retries 3 times) and suceeding on
> the second or 3rd attempt. (See xfer 338, retry 0, followed by a 'soft
> error corrected' with the same xfer number 10 seconds later. This is
> the retry suceeding).

Ah, interesting point.  I find this confusing, because I thought an
uncorrectable read error would, for disks I've dealt with, cause the
sector to be marked as permanently failed and pending reallocation.

I also didn't realize that wd(4) would issue aother read when there is a
failure, but maybe that's in zfs glue code.

> This sits below ZFS and therefore ZFS never sees the error. If the
> read failed 3 times you'd probably get a data error in ZFS.

That makes sense.

>>    5 200  140     yes online  positive    Reallocated sector count    0
> I was expecting to see this value greater than 0 if the drive was
> failing, is the drive bad or the cabling?

Sectors get marked as failed, and then they actually get reallocated
when you write.
I bet after a dd of /dev/zero that will go up.

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