Is 650 GB per day between hard disks connected by 1 GBit ethernet ok?

[svenha]

Two 8 TB HDD, connected over 1 GBit ethernet, fast CPUs on both sides. The initial backup took 11.5 days for 7.5 TB of data (speed: 650 GB per day). btrbk is version 0.32.6, package from Ubuntu 22.04.

I wonder whether I see a typical speed of a full btrbk backup or have a hardware problem or ...