Disaster Recovery File

Hi,

I use Symantec backup exec 2012 on a windows 2008 server (Domain controller, active directory and File server)

I make a complete backup of my server every day on a tape drive.

My question is :

I need to save each *.DR file for each backup ? 1 DR file per day ?

For example, If I have to restore the backup of Friday, I have to use the specific DR file of Friday ? Or it doesn't matter if the system C: or the partitions size doesn't change.

What kinds of information contain DR file ?