You NEED to remove the "conv=noerr", otherwise dd will not stop on io error.
Hence
ctrl-C (
if need be).
I think dd behaves differently than you are expecting. If it hits an error that stumps it (hangs dd, either temporarily or permanently) then ctrl-c won't save you. It'll be blocking in the kernel until it finishes the block it was reading. THEN ctrl-c may stop it. But it's been my experience that unless you're using a very small block size (512 etc) then you're in for an awful long wait, as each disc block (512) may take 1-2 minutes to pass. If your dd block size is 1mb, it could be 20 minutes or more before it releases with ctrl-c. Some block errors never complete and block until killed.
The reason to not use conv=noerror is that if it gets an error (that passes quickly, say one bad disk block in the entire dd block) then it will display the io error to console, but with conv=noerror, it WON'T STOP, and will NOT return an error code when dd finally finishes. This isn't usually how you want it to behave when looking for errors, unless you are trying to count how many you have. (I usually consider one to be more than enough!) If you omit that conv, dd will stop at its first bad block encountered, and will return an error code.
(fyi, dd pads unreadable blocks with zeros if you use conv=noerror)
