Time Machine backups are great, but very slow when a large amount of data/files needs to be transferred (such as the initial back-up). As desgined by Apple the Time Machine background proces is running in a very low CPU priority, giving all other running applications en services priority.
With the following Terminal command you can temporary speed up the Time Machine backups:
sudo sysctl debug.lowpri_throttle_enabled=0
The command prevents Time Machine’s backup process assuming a low CPU priority, allowing backups to complete more quickly.
The command is not persistent and will become inactive after a reboot. If you want revert to the default setting without a reboot:
sudo sysctl debug.lowpri_throttle_enabled=1
Searching for more Time Machine tweaks? Check this!
I tried this on a ~105 GB backup. I was already partly through the back up, and didn’t notice any speed increase. Will try before I start a backup.