Windows 7 system image: Previous increment not visible in Explorer

Question

I tried out the backup tool built into Windows 7 Pro x64. In the help text, it says: "If you're saving your system images on an internal or external drive, or on CDs or DVDs, you can keep several versions of system images."

What I did as a test:

1. Attached a USB 3 HDD with ca. 600 GB of free space.

2. Using Windows 7's Backup and Restore, created a system image of the ca. 200 GB system drive. This includes the two standard Windows 7 partitions: (C:) and System Reserved:

   

3. Made a small change, adding text in a file, which would allow me later to compare different increments.

4. Made another system backup using Backup and Restore.

Now, when I look at the USB drive, I only find one .vhd file per partition, with time stamp of the backup from step 4:

Does this mean that no increment has been created, i.e. the first backup has been overwritten? Can there perhaps be only one increment per day?

Answer 1

I have found the answer in a 2009 TechNet article “Learn more about system image backup”:

During the first backup, the backup engine scans the source drive and copies only blocks that contain data into a .vhd file stored on the target, creating a compact view of the source drive. The next time a system image is created, only new and changed data is written to the .vhd file, and old data on the same block is moved out of the VHD and into the shadow copy storage area. Volume Shadow Copy Service is used to compute the changed data between backups, as well as to handle the process of moving the old data out to the shadow copy area on the target. This approach makes the backup fast (since only changed blocks are backed up) and efficient (since data is stored in a compact manner). When restoring the image, blocks will be restored to their original locations on the source disk. If you want to restore from an older backup, the engine reads from the shadow copy area and restores the appropriate blocks.

In a nutshell: Only the last backup is displayed in Windows Explorer. Previous increments are stored in the shadow copy storage area on the backup medium.

How VHDs from previous increments can be accessed for attaching using Windows 7’s Disk Management is not clear to me.