Post El Capitan backup from local hd to usb extremely slow

After upgrade, backup of my downloads folder to a folder on my USB 2.0 HD said "preparing", then locked up totally and wouldn't complete. I had to force finder to close to get rid of the progress bar. Similarly, I tried to use Time Machine to copy a minimal amount of data to portable USB HD and it said it would take like 21 hours to complete. Something has changed dramatically since Yosemite to cause this. It would appear from different threads that others have noticed similar issues.