5. vCloud Resource Design : 5.9 Snapshots : 5.9.1 Snapshot Architecture
5.9.1 Snapshot Architecture
A snapshot preserves the state and data of a virtual machine at a specific point in time:
*The state includes the virtual machine’s power state (powered-on, powered-off, suspended).
*The data includes all of the files that make up the virtual machine.
Snapshots work by creating delta copies (point-in-time) of the specified virtual machine files. The following figure provides a high-level illustration of how the process works.
Figure 33. Snapshot Processing

Each snapshot is composed of the following files, where <vm> is the name of the virtual machine and <number> identifies the specific snapshot:
*<vm>-<number>.vmdk and <vm>-<number>-delta.vmdk.
A collection of .vmdk and -delta.vmdk files for each virtual disk is connected to the virtual machine at the time of the snapshot. These files are referred to as child disks, redo logs, or delta links. Child disks can later become parent disks for future child disks. From the original parent disk, each child constitutes a redo log that points back from the present state of the virtual disk, one step at a time, to the original one.
NoteThe <number> value might not be consistent across all child disks from the same snapshot. The file names are chosen based on filename availability.
The .vmsd file is a database of the virtual machine's snapshot information and the primary source of information for the snapshot manager. The file contains line entries that define the relationships between snapshots as well as the child disks for each snapshot.
These files record the memory state at the time of the snapshot.