I've seen bits of this covered in other posts but haven't found one PuTTY specific. (Or maye I should get my eyes checked). Never the less there are many reasons you want to use a Key Pair to access your unRAID server via SSH compared to using just a username and password.   This is especially true if you'd like to access your server via the internet. Another benefit to doing this is the use of Tunnels. Using SSH you can tunnel into just about anything. Take this example below.