About Snapshots

A virtual machine (VM) snapshot is a record of a running VM at a point in time. When you take a snapshot of a VM, its storage information (the data on the hard drive) and metadata (configuration information) is also saved. Where necessary, I/O on the VM temporarily halts while you take the snapshot to ensure that the snapshot captures a self-consistent disk image.

You can create snapshots without first shutting down the VM. This behavior is different to VM exports. A snapshot is similar to a normal VM template but it contains all the storage and configuration information for the original VM, including networking information. Snapshots provide a fast way of creating templates to export for backup purposes and then restore, or to use to quickly create VMs.

Snapshots are supported on all storage types.

Types of snapshots

XenCenter supports the following types of VM snapshot:

  • disk-only
  • disk and memory

Note:

In Citrix Hypervisor 8.0 and earlier versions, quiesced snapshots are also supported.

For more information, see Take a VM Snapshot.

Disk-only snapshots

Disk-only snapshots store a VM’s configuration information (metadata) and disks (storage), allowing them to be exported and restored for backup purposes. This type of snapshot is crash-consistent and can be performed on all VM types, including Linux VMs.

Disk and memory snapshots

In addition to saving the VM’s metadata and disks, disk and memory snapshots also save the VM’s memory state (RAM). Reverting to a disk and memory snapshot does not require a reboot of the VM, and VMs can be running or suspended when the snapshot is taken. Disk and memory snapshots can be useful if you are upgrading or patching software, or want to test a new application, but also want the option to be able to get back to the current, pre-change state (RAM) of the VM.

Quiesced snapshots

Important:

In Citrix Hypervisor 8.1 and later, quiesced snapshots are not supported.

Quiesced snapshots take advantage of the Windows Volume Shadow Copy Service (VSS) to generate application-consistent point-in-time snapshots. The VSS framework helps VSS-aware applications (for example Microsoft Exchange or Microsoft SQL Server) flush data to disk and prepare for the snapshot before it is taken. Quiesced snapshots are, therefore, safer to restore, but can have a greater performance impact on a system while they are being taken. They might also fail under load, so more than one attempt to take the snapshot might be required.

Accessing orphaned snapshots

If you take snapshots of a VM and later delete the original VM, you can still access those snapshots in the Resources pane. Switch to Objects view in the Navigation pane and then expand the Snapshots group to see all available snapshots.