Since no-one's mentioned it yet, I've experienced super slow initial backups too, but found disabling the built in throttling sped things up so that it actually

Since no-one's mentioned it yet, I've experienced super slow initial backups too, but found disabling the built in throttling sped things up so that it actually completes more quickly: sudo sysctl debug.lowpri_throttle_enabled=0 It seems to reset itself automatically.