Creating a drive clone backup

I have two physical drives - running Windows 7. I want to create a clone of the primary drive as an ofsite backup for total drive failure. The last time I did this I vaguley remember having issues - that there are 2 ways that WIndow 7 can boot - also - do I have to do something to clone the drive serial number as WINdows 7 may have that enbedded to prevent an  "illegal" copy.

Also - I posted this in the 2015 forum by mistake - I'm actually running 2014,  but have a 2015 license - are there any risks to upgrading?