dd was useful in the old days when people used tapes (when block sizes mattered) and when simpler tools such as
cat might not be binary-safe.
dd if=/dev/sdb of=/dev/sdc is a just complicated, error-prone, slow way of writing
cat /dev/sdb >/dev/sdc. While
dd still useful for some relatively rare tasks, it is a lot less useful than the number of tutorials mentioning it would let you believe. There is no magic in
dd, the magic is all in
Your new command
sudo dd if=/dev/sdb bs=128K | pv -s 3000G | sudo dd of=/dev/sdc bs=128K is again needlessly slow and complicated. The data is read 128kB at a time (which is better than the
dd default of 512B, but not as good as even larger values). It then goes through two pipes before being written.
Use the simpler and faster
cat command. (In some benchmarks I made a couple of years ago under Linux,
cat was faster than
cp for a copy between different disks, and
cp was faster than
dd with any block size;
dd with a large block size was slightly faster when copying onto the same disk.)
cat /dev/sdb >/dev/sdc
If you want to run this command in
sudo, you need to make the redirection happen as root:
sudo sh -c 'cat /dev/sdb >/dev/sdc'
If you want a progress report, since you're using Linux, you can easily get one by noting the PID of the
cat process (say 1234) and looking at the position of its input (or output) file descriptor.
# cat /proc/1234/fdinfo/0
If you want a progress report and your unix variant doesn't provide an easy way to get at a file descriptor positions, you can install and use
pv instead of