I know I can rsync data from teamcity when it is offline. I have read in your backuop documents to never copy or backup the data directory while teamcity is running. I assumed this just means that you would not get a valid backup if you did try and copy\backup while teamcity is running. Can you confirm that backing up data on a running teamcity instance will not harm the instance that is running?
My overall goal is to backup a huge directory using rsync while teamcity is running to help alleviate downtime. Once the majority of data is transfered I would stop teamcity and re-run rsync to get the differential data. This will give me a complete backup for the new instance I am migrating too but I wanted to be sure that it would not hurt my running instance due to your warnings about never copy\backup while teamcity is running. I assume it would have no ill side effect but I wanted to make sure before proceeding.