I assure you, rsync can tank a highly tuned db environment. 'updatedb', which updates the db 'locate' uses under linux, running in its cron, can cause issues.

It all depends upon how much headroom you have, the type of io activity, etc. I've operated systems under consistent 80% io load with massive datasets at the time, under spinning disks.

Running rsync would be madness on such a system. I know. I only did it once.