Transfering files in the background via
rsync is possible via
nohup command and some other workarounds.
These don't really work when your transfer takes days (>50TB of data) because the background job might get killed by the system.
In order to create a persistent session we need to use
Create a ssh key and upload it to the server you want to transfer from.
ssh-keygen -t ed25519
ssh-copy-id -i ~/.ssh/id_rsa.pub [your_old_server.domain.com]
Create a new session and run
tmux new -s [your_session_name]
rsync --avhPW --stats [your_old_server.domain.com]:[/source/path/] [/destination/path]
Detach from session
CTRL+B and then
D. You session will detach and run in background.
To get back into your session just:
tmux a -t [your_session_name]