Hi 
Does has Elk Stack on single Node some disadvantages ? If yes, which? (if you have logs about 4 Gb a day)
thank you
The obvious disadvantage is you have a single point of failure.
why it should be this a disadvantage ..? In this case I dont need to send the logs out of the node
Same reason someone might want a reserve parachute.
If you consider the consequences of a failure are large then you don't rely on a single instance.
Having more than one node also means you can service higher volumes of concurrent queries.