Hi Peter,
> $ sudo dd if=/dev/sdb of=./webiopi3.img
How did you identify it's /dev/sdb?
> dd: error reading '/dev/sdb': Input/output error
That shouldn't happen.
> - mounted
Yes, you ideally want to do it unmounted, as you initially tried.
> 129504+0 records in
> 129504+0 records out
...
> 86240+0 records in
> 86240+0 records out
Looks like there's an intermittent problem reading from the card, or
through the network of USB cables, hubs, etc., to get to it. Can you
plug it in `closer' to the machine, e.g. a built-in card slot?
You could keep repeating it, unmounted, until it succeeds without I/O
error. Or try another PC, even if you `of=/dev/null', to see if that
can read it without error? Or try a card you don't want to image, just
so you know it's possible in theory on that hardware?
> it imaged at 12.1GB from a 16GB disk which does sound a bit large.
Small? 16 GB disk should give 16 GB image, unless you're compressing.
And 16 GB is 14.9 GiB if you're switching units in your measuring.
Another way to check, having removed and re-inserted the card so Linux
has forgotten all about it from its buffer cache, is to take its digest
and that of your image file.
sha1sum /dev/sdb disk.img
They should match. And writing down a prefix of the digest somewhere
means you'll be able to check each hasn't changed in the future.
Cheers, Ralph.
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