6.0

File Description
vmname-number.vmdk and vmname-
number-delta.vmdk
Snapshot le that represents the dierence between the current state of the virtual
disk and the state that existed at the time the previous snapshot was taken.
The lename uses the following syntax, S1vm-000001.vmdk where S1vm is the
name of the virtual machine and the six-digit number, 000001, is based on the
les that already exist in the directory. The number does not consider the number
of disks that are aached to the virtual machine.
vmname.vmsd
Database of the virtual machine's snapshot information and the primary source of
information for the Snapshot Manager.
vmname.Snapshotnumber.vmsn
Memory state of the virtual machine at the time you take the snapshot. The le
name uses the following syntax, S1vm.snapshot1.vmsn, where S1vm is the
virtual machine name, and snapshot1 is the rst snapshot.
N A .vmsn le is created each time you take a snapshot, regardless of the
memory selection. A .vmsn le without memory is much smaller than one with
memory.
Snapshot Limitations
Snapshots can aect virtual machine performance and do not support some disk types or virtual machines
congured with bus sharing. Snapshots are useful as short-term solutions for capturing point-in-time virtual
machine states and are not appropriate for long-term virtual machine backups.
n
VMware does not support snapshots of raw disks, RDM physical mode disks, or guest operating
systems that use an iSCSI initiator in the guest.
n
Virtual machines with independent disks must be powered o before you take a snapshot. Snapshots of
powered-on or suspended virtual machines with independent disks are not supported.
n
Snapshots are not supported with PCI vSphere Direct Path I/O devices.
n
VMware does not support snapshots of virtual machines congured for bus sharing. If you require bus
sharing, consider running backup software in your guest operating system as an alternative solution. If
your virtual machine currently has snapshots that prevent you from conguring bus sharing, delete
(consolidate) the snapshots.
n
Snapshots provide a point-in-time image of the disk that backup solutions can use, but Snapshots are
not meant to be a robust method of backup and recovery. If the les containing a virtual machine are
lost, its snapshot les are also lost. Also, large numbers of snapshots are dicult to manage, consume
large amounts of disk space, and are not protected in the case of hardware failure.
n
Snapshots can negatively aect the performance of a virtual machine. Performance degradation is based
on how long the snapshot or snapshot tree is in place, the depth of the tree, and how much the virtual
machine and its guest operating system have changed from the time you took the snapshot. Also, you
might see a delay in the amount of time it takes the virtual machine to power-on. Do not run production
virtual machines from snapshots on a permanent basis.
n
If a virtual machine has virtual hard disks larger than 2TBs, snapshot operations can take signicantly
longer to nish.
Taking Snapshots of a Virtual Machine
You can take one or more snapshots of a virtual machine to capture the seings state, disk state, and
memory state at dierent specic times. When you take a snapshot, you can also quiesce the virtual machine
les and exclude the virtual machine disks from snapshots.
When you take a snapshot, other activity that is occurring in the virtual machine might aect the snapshot
process when you revert to that snapshot. The best time to take a snapshot from a storage perspective, is
when you are not incurring a large I/O load. The best time to take a snapshot from a service perspective is
when no applications in the virtual machine are communicating with other computers. The potential for
Chapter 3 Virtual Machine Management with the VMware Host Client
VMware, Inc. 75