6.7

Snapshot Behavior
Taking a snapshot preserves the disk state at a specific time by creating a series of delta disks for each
attached virtual disk or virtual RDM and optionally preserves the memory and power state by creating a
memory file. Taking a snapshot creates a snapshot object in the Snapshot Manager that represents the
virtual machine state and settings.
Each snapshot creates an additional delta .vmdk disk file. When you take a snapshot, the snapshot
mechanism prevents the guest operating system from writing to the base .vmdk file and instead directs all
writes to the delta disk file. The delta disk represents the difference between the current state of the
virtual disk and the state that existed at the time that you took the previous snapshot. If more than one
snapshot exists, delta disks can represent the difference between each snapshot. Delta disk files can
expand quickly and become as large as the entire virtual disk if the guest operating system writes to
every block of the virtual disk.
Snapshot Files
When you take a snapshot, you capture the state of the virtual machine settings and the virtual disk. If
you are taking a memory snapshot, you also capture the memory state of the virtual machine. These
states are saved to files that reside with the virtual machine's base files.
Snapshot Files
A snapshot consists of files that are stored on a supported storage device. A Take Snapshot operation
creates .vmdk, -delta.vmdk, .vmsd, and .vmsn files. By default, the first and all delta disks are stored
with the base .vmdk file. The .vmsd and .vmsn files are stored in the virtual machine directory.
Delta disk files A .vmdk file to which the guest operating system can write. The delta disk
represents the difference between the current state of the virtual disk and
the state that existed at the time that the previous snapshot was taken.
When you take a snapshot, the state of the virtual disk is preserved, the
guest operating system stops writing to it, and a delta or child disk is
created.
A delta disk has two files. One is a small descriptor file that contains
information about the virtual disk, such as geometry and child-parent
relationship information. The other one is a corresponding file that contains
the raw data.
The files that make up the delta disk are called child disks or redo logs.
Flat file A -flat.vmdk file that is one of two files that comprises the base disk. The
flat disk contains the raw data for the base disk. This file does not appear
as a separate file in the Datastore Browser.
vSphere Virtual Machine Administration
VMware, Inc. 244