About the pv overhead, I sent a note to the pv author saying that on Linux at least the transfer function could take advantage of the splice system call. Splice "copies" data from one file descriptor to another file descriptor, avoiding having to copy the data from the kernel to userspace and back.

On FreeBSD (and maybe Mac OS X) you can press Control-T to send a SIGINFO signal (non-standard extension. This prints out how far dd has gotten (and perhaps other FreeBSD utilities too).

You may need to setup your terminal to do that with:

    stty status '^T'

fsck also responds to SIGINFO by printing its status. I had to hack up rsync to do it (http://jcs.org/patches/rsync-show_current_file.diff), and I wish more utilities supported it by default.

N.B. also that dd on osx will EXIT IMMEDIATELY if sent a SIGUSR1. It double-sucks because one tends to do this on long-running dd processes that you're wondering are done yet...