There are many ways to monitor block device performance: dstat and iostat, heck, even sar will give you data on block device I/O rates. Unfortunately, I don't know of any good spur-of-the-moment tools for monitoring the performance of a character device like a tape drive.
I know there are tools to monitor performance if you remember in advance to do it (pv, dd + SIGUSR1, probably others), but say you're 2 hours into a job that might be 3 hours or 30 hours depending on the performance, and you don't know which it is.
The only thing I can think of is some elaborate use of strace or similar, parsing the output for bytes written, maybe with timestamps. Is there a commonly used tool that I've forgotten or never heard of?
