Backup levels

Hello!
Today we had a bad experience with one of our engineers who decided to free some disk space at the server with uninstalling SQL server software. In this situation we had to use backup to restore the server functionality. I want to share our backup levels.
Most of our servers work at the virtual machines this give as an opportunity to have first level of backup with hypervisor. It locks virtual machines files from changing at the storage (make a snapshot) and store them from time to time. This is very fast method. We can make snapshots for backups every minutes. Note that not snapshots of the original virtual machine are used as backup but a copy of the machine with snapshots (because snapshots slower the virtual machines). This method gives as backups that are made several times a day and we can recover the server not only to the "night state". This is "external backup". It can be done even is virtual machine hang. It store backups inside the block storage of the hypervisor.
The second level is the backup software in the host operation system. It locks filesystem for backup and store the changes that was made in the OS to the external network datastore. In our case this is a file storage. This method is slower than first and run once a day at night. But it use a different method to access the data for backup.
The last one is the application backups. Some applications are able to make is own backups. For example databases. If they can - they must do them.
The first and the second level backups in most cases can restore virtual machine (second one can restore physical server too) to the time when backup was made. But it will look for server like it was hard reseted. It can not run properly after that.
The third level make consistent backups that store restorable data all the time. But it didn't store all the server operation system.
PS: Of you need to free some space to store backups - think about extending of your storage. More space for backups maybe better then more space for user data.
PPS: Test your backups from time to time regularly.