[wellylug] DD no go

[David Antliff]

On Fri, Apr 4, 2008 at 5:56 PM, David Chord <gnome at gnome.co.nz> wrote:
>  Command line is dd if=/dev/sda of=/dev/sdb
>
>  Error is "dd: writing to `/dev/sdb' : Input/output error
>  8395977+0 records in
>  8395976+0 records out
>  4298739712 bytes (4.3 GB) copied, 701.827s, 6.1 MB/s
>
>  After the 2nd time I formatted sdb to fat32 (was a blank disk on the first
>  run), no luck.

First of all, you shouldn't format a DISK device (e.g. sdb) at all -
you should only ever format PARTITIONS (which are subdivisions of a
disk, e.g. sdb1, sdb2). That said, if you dd to the disk device you
overwrite anything that was there anyway, so it's redundant formatting
it with anything.

Secondly, that's normally what happens when you run out of space on
the destination device, but after only 4.3GB? How big is the disk
drive? I'm guessing much bigger than 4.3GB... so it sounds like you
might have a problem with the destination disk?

Thirdly, there's nothing special that comes to mind about the number
4298739712, in case you were wondering.

Stated for clarity: a record size is 512 bytes (by default).

Try this and see if it does the same thing (make sure your 'of' device
is correct as it will overwrite anything there!):

# dd if=/dev/zero of=/dev/sdb seek=8395975 count=5

That skips to somewhere near the place you have a problem, so it won't
take so long to fail if it's going to.
Might be worth trying to write beyond that sector too:

# dd if=/dev/zero of=/dev/sdb seek=8395978 count=100

There's a program called 'ddrescue' that does a smarter thing by
retrying errors. However if it has to do this on your destination disk
I'd be worried about the integrity of your backup device...

Can you try a different destination disk?

-- 
David.