Just bought ds418. I have a 3tb, 2tb and 2tb drive. Once these are installed can I add another hd without disrupting the data on the other drives, and when I add a 10tb just slot it in format it then move files from the two 2tb onto the 10tb then remove them? Is the os stored on one of the hd? If so removing hd will bigger it? I'll use the 3tb for music storage. I'll be use individual drive layout. What if I install the 3tb first then setup the Nas install firmware the os is installed to that and then add the two 2tb?