I mean if you use the NoSQL than make any upgrades/ replace one machine will not have any effect on user due to its distributed nature is RDBS able to behave in similar way in the future?
This a question usually asked by programmers who don't truly understand data architecture. The right tool for the job...but one still has to fully understand the tool to obtain the greatest benefit. Simple? It doesn't get any simpler than a well designed RDBMS...unfortunately, that's a rare occurrence.