To make a backup copy is not all!

We are for more than 2 months testing and preparing one server. It will be a hosting server. Yesterday we wanted to update one of the applications on the server but for some reason the update damaged the system. After trying many ways to solve the problem we concluded that the best thing to do was to restore a backup or to reinstall the server!
We tried restoring the backup first and we discovered that the backup process had a problem... So we were unable to restore some important system data that helps to connect databases and other services. The conclusion of the 2 days adventure was a full reinstall of the server.
That makes us remember something very important! Before using a server on production, it means on real work, a full system backup should be restored in order to find errors.
We were lucky that this server was in a testing period and stored any important thing. We would be only capable of restoring documents and files on the file system but not within the databases.
"To have backup copies is not all! The important thing is to simulate the need of a full system restore and try if it works 100%"