Updating our old mac, 10.5.8. New external drive slowed/.stalled once a quarter was done.

Very new at this. The touro external 1tb needed to be re formatted and something to do with the petition. Did this and then started the time machine. Worked great but has stalled on 46gb of 267gb.I thought it had stopped but doing it extremely slowly. Any answer would be of great value

Cheers

Ben