Windows – How to test a restore from a Windows 7 backup

This is doable using Virtual Box. Install Virtual Box, Create a New VM with the setting required for the new system, Open the settings for the new VM and add a CD drive using either an ISO of your rescue media or the CD drive on your computer, and finally start the VM and go through the process.

It should be pretty straightforward, if all you're doing is testing if the rescue disk does what it's supposed to do.

Does WBA backup the same files over and over again rather than just updating existing ones?

Yes, each update contains whole files. If one always updates the same files, then these same files are saved again and again.

Why does my backup file size accumulate when I am not adding anywhere near that amount of new data?

Because the same files are backuped again and again.

What is in an old backup?

A backup contains files and a directory that lists their placement.

Does an old backup contain anything that a new backup doesn't?

Not necessarily. An incremental backup may possibly only contain files that are superseded in newer updates, but there is no way of knowing that.

Can WBA be configured to automatically delete backups that are X days old?

Only an entire backup set can be deleted, as one can never know which incremental update is useful (meaning contains a file that is found nowhere else).

Windows 7 Backup has a feature which allows you to manage backup disk space. On the Backup and Restore Center page, look for the "Manage Space" link. You will find it right under the target description.

The following blog post walks you through the UI and the space management options available: Managing backup disk space.

Windows Backup takes full backups of data from time to time. If you want for example to set up full weekly backups, this registry entry is said to tweak full backup frequency:

Path: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsBackup\AutomaticFullBackup
Name: TimePeriodInDays
Type: DWORD
Value: the default value is 365. Set it to 7 for weekly full backup.

However, there are reports that this may not work as expected.

I remark that there have been many problems reported with Windows Backup on this forum. There are too many gotchas and one risks finding that the backup taken is unusable at the worst possible time.

I really suggest using instead a third-party solution, of which there are many, as being much safer and easier to use. See Best Free Backup Program (including the comments).