[OpenIndiana-discuss] System disk corruption

[Robin Axelsson]

On 2012-02-19 21:23, Richard Lowe wrote:
> Vague recollection that the pool level is errors that weren't
> recovered, so possibly two of them on the device were ditto'd
> metadata?  (I'm very unsure on both counts).
>
> Otherwise, as Chris said, iostat is particularly difficult to trust.
> No matter what the error (even if, indeed, the drive or transport)
> there's no guarantee (or in my bitter experience even likelyhood) of
> formal errors occurring to go with the data being bad.
>
> -- Rich
>
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>

Maybe the iostat "behavior" depends on the controller it monitors. Some 
controllers such as the AMD SB950 in my case may not be as transparent 
with errors as the LSI 1068e operating in IT mode.

Still, I find this to be too much of a coincidence. It is evident that 
ZFS is not very good to use without disk redundancy. I'll try to add a 
mirror to the system pools as soon as possible. It would be great if 
there were some kind of software that could be set up to generate .par2 
files (with x% data redundancy) on-the-fly to protect files on hard 
drives without disk redundancy (RAID=0).

I couldn't recover the image file with cp but I learned in the process 
that it is possible with dd. 'dd if=infile of=outfile conv=noerror,sync' 
could do it. Then I discovered ddrescue which did *exactly* what I 
expected cp to do. I just entered:

# ddrescue /path/to/corrupted/file /path/to/recovered/file 
/path/to/logfile.log

all paths were even in the same vdev. In the process the vdev became 
'DEGRADED' even though no additional corruption occurred. So I did a 
scrub afterwards and 'zfs clear':ed the error afterwards. I did an fmadm 
repair to tell fma about it. Perhaps I should fmadm reset zfs-diagnosis 
and zfs-retire as well.

Neither par2 nor ddrescue are included with OpenIndiana, I downloaded 
and installed them manually from the opencsw.org repository. I would 
strongly recommend to have such tools included with OI.

The package names are

CSWpar2cmd
CSWddrescue

Their dependencies are the following:

CSWcommon
CSWgcc2g++rt
CSWgcc2corert

and

CSWcas_texinfo

Robin.