6.0

Each snapshot creates an additional delta .vmdk disk le. When you take a snapshot, the snapshot
mechanism prevents the guest operating system from writing to the base .vmdk le and instead directs all
writes to the delta disk le. The delta disk represents the dierence 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 dierence between each snapshot. Delta disk les 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 seings 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 les that reside with the virtual machine's base les.
Snapshot Files
A snapshot consists of les that are stored on a supported storage device. A Take Snapshot operation
creates .vmdk, -delta.vmdk, .vmsd, and .vmsn les. By default, the rst and all delta disks are stored with the
base .vmdk le. The .vmsd and .vmsn les are stored in the virtual machine directory.
Delta disk files
A .vmdk le to which the guest operating system can write. The delta disk
represents the dierence 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, which prevents the
guest operating system from writing to it, and a delta or child disk is created.
A delta disk has two les, including a descriptor le that is small and
contains information about the virtual disk, such as geometry and child-
parent relationship information, and a corresponding le that contains the
raw data.
The les that make up the delta disk are referred to as child disks or redo
logs. A child disk is a sparse disk. Sparse disks use the copy-on-write
mechanism, in which the virtual disk contains no data in places, until copied
there by a write operation. This optimization saves storage space. A grain is
the unit of measure in which the sparse disk uses the copy-on-write
mechanism. Each grain is a block of sectors that contain virtual disk data.
The default size is 128 sectors or 64KB.
Flat file
A -flat.vmdk le that is one of two les that comprises the base disk. The at
disk contains the raw data for the base disk. This le does not appear as a
separate le in the Datastore Browser.
Database file
A .vmsd le that contains the virtual machine's snapshot information and is
the primary source of information for the Snapshot Manager. This le
contains line entries, which dene the relationships between snapshots and
between child disks for each snapshot.
Memory file
A .vmsn le that includes the active state of the virtual machine. Capturing
the memory state of the virtual machine lets you revert to a turned on virtual
machine state. With nonmemory snapshots, you can only revert to a turned
o virtual machine state. Memory snapshots take longer to create than
nonmemory snapshots. The time the ESX host takes to write the memory
onto the disk is relative to the amount of memory the virtual machine is
congured to use.
A Take Snapshot operation creates .vmdk, -delta.vmdk, vmsd, and vmsn les.
vSphere Single Host Management - VMware Host Client
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