I disagree - to a point.
I agree that a snapshot is NOT a backup. However, a backup that is taken that is based upon a snapshot is perfectly reliable.
Before a snapshot is taken, Windows stops all data from being written to the ACTIVE filesystem and flushes any writes that are in flight to give you a consistent point in time. Only then is the snapshot taken and the backup is then in turn based upon the contents of the snapshot which remain consistent and do not change during the entire duration of the backup.
I'm giving the highly simplified version here, because there is actually a lot more involved. For databases, mail servers, etc., those types of programs are VSS aware and take special actions when VSS is preparing to take a snapshot so that those applications can guarantee consistency down to the individual transaction, but that's a complicated topic that we don't need to go into here.
So, while a snapshot is not a backup by itself, a snapshot can allow you to create a reliable, consistent snapshot.
Please be aware that I am making the assumption that everything is working properly. As with everything else, things can break. But then again, things can break even if you are doing a backup where the OS is not even running. Nothing is perfect
