cp command is not suitable for large data transfers between two hard drives. It makes about 10..100KB/sec. Obviously, it will take 29 hours to copy 10GB with 100KB/sec.
There are many ways to speed up copying process -- using USB, Firewire, Ethernet etc. But if everything is done on a local machine, rsync is very effective and simple to use. For example, the following shows how to copy files over the virtual loopback device:
$ mkdir -p /mnt/hdd $ sudo mount /dev/sdbX /mnt/hdd $ rsync -az user@localhost:/some/folder/* /mnt/dest-hdd/
a("archive mode") option takes care of permissions, ownership, group, symlinks and so. z instructs rsync to use compression.
