why can;t remote media server from nbemmcmd?

I would not recommend even thinking of continuing to run your environment on CentOS master - they will not be supported (sorry but out of my control) and in the event of some major issue you risk losing everything, because, even with best efforts, if the OS is unsupported there are some things that cannot be fixed.

If you have 'legal' reasons to hold backups / financial data etc .... you are running a major risk and would most likely not pass any audit requirements.