One of the most common problems we hear is that a full backup takes longer than one night to complete (The slow backup problem).  Here at Highly Reliable Systems, we’ve tested a variety of backup software and have found that imaging based products (as opposed to file based) provide the best backup performance.  A product like StorageCraft’s Shadowprotect will do a block level copy of every occupied sector of your disk, providing the best backup speed and smaller backup windows.  The product now supports virtualization, meaning they have special licensing for protecting multiple Virtual machines running on a single piece of hardware.  This article discusses the virtualization  options:

In addition to using block level imaging, products like Shadowprotect allow the  use of incremental backups that can be periodically rolled up into a single image file (often referred to as synthetic backup).  This overcomes the old concern of having to restore from multiple tapes or files and verifies data integrity in a single file.