After the 50,129^th^ time today that Time Machine tried to start backing up over 1 GB of data to my home server, I decided to figure out why instead of repeatedly hitting cancel. It turns out that the majority of the data TM wanted to copy was being created by my other favorite backup solution, Backblaze.
Backblaze stages files for upload to their servers in
/Library/Backblaze/bzdata. If you’re using both backup systems, I’d highly recommend that you add that folder (or
/Library/Backblaze, as I did) to Time Machine’s ignored folder list. Otherwise, you’re just wasting space and valuable CPU cycles.