Why is it taking days to copy 80gigs from internal to external USBdrive takes days

I have an internal hard drive hooked up as a slave to a computer and a
USB external connected. I am trying to copy about 80 gigs to the
external from the slaved internal. It has literally been running 10
hours and has copied less than quarter of it based on the progress
bar. It is also claiming it will take another 2 days 23 hours to
complete. It sits on one file for as much as 5 minutes or more before
on to the next one. Is this unusually slow. I've set the the external
to Optimize Performance in Device Manager. Oh and this is being done
on Windows XP and both the internal slave and the external drive are
NTFS partitions. Any ideas why it is taking so long?

Thanks in advance,
Adam