Is there something special about Time Machine and SD that explains this?
 

Usually when I do a smart update, SD will take substantially less time than an erase and copy...often a difference of hours for, say, a 500GB data volume.

I have a 1.5TB Time Machine volumen that has about 1.1TB used. I wanted to replace that drive with a 2TB drive. I started to copy the TM volume, and about 7 hours in the thermometer was showing about 90% done and about 6Million of the 8Million files done. All good.

There was a high wind warning in our area, and I decided to stop the copy and shut down the machine. I then picked it up the next day. I expected that SD would fly through the part already backed up. Instead, the backup took 5 hours, yet only 2.5GB was reported as copied.

This puzzles me. Is this expected behavior for a TM volume?

Yes. There are millions and millions and millions of hard links that we have to track, match and recreate. It's complex and time consuming...

Thanks for the quick reply!