I have a backup routine set up, and would like to use rsync to make a copy to another server. My question is whether rsync will be able to move without breaking files with the routine enabled.
Taking backups via file system snapshots is not supported and will most likely not work unless you are on an old version (?). Instead use the snapshot and restore APIs.
I'm using Elasticsearch 6.8 where I have a routine that generates snapshot daily. If you use rsync to move the snapshot and start taking another snapshot while rsync is active, won't rsync corrupt the files or will it work properly?
Copying a snapshot repo won't reliably work if done concurrently with taking another snapshot -- snapshots comprise multiple files and files are shared between multiple snapshots so it's very likely you'll end up missing some vital files.
See https://github.com/elastic/elasticsearch/issues/54944 for a possible solution to this, but that's not something that's being worked on at the moment.