send serial monitor to server and save data in hdd I'd like stream data to my disk via serial and then send it to a central server. e.g. log an event.
i wouldn't use any separate modules.
Any helps appreciated.
You could look and see if there was any data logging libraries already written or you would need to develop a function that wrote to a file held on an SD card.  There are plenty of SD libraries.

If you mean you have a computer connected to the serial connection from the ATMega then there are probably logging programs out there, some terminal monitors save what they receive.