Virtual Machine Backup
Types of Backups

• Agent-based backup
• Backend storage replication
• Manual snapshots from XenCenter
• Scripted snapshots through XenAPI
• Enhanced backup enablement with third-party backup product

Agent-based Backup - Agent-based backup is the traditional way of performing file- and full-system backups. You install a backup agent on the operating system of the virtual machine and then define a policy using the backup agent software so that the agent can copy files to the backup server.

Benefits	Considerations
Proven technology and approach Protects investment in current backup solution and knowledge Easy file-level restoration Agents tailored to specific applications Can be performed while virtual machines are running	Long backups can affect service-critical virtual machines Not specifically geared for virtual machines

Backend Storage Replication - When you use XenServer with a shared Storage Repository (SR), you can use a backend storage replication mechanism. It is recommended by Citrix that you use backend storage replication to augment an agent-based or snapshot-based virtual machine backup.

Benefits	Considerations
Optimizes replication for storage solution Provides both virtual machine backup and disaster recovery Augments other virtual machine backup approaches	Additional hardware and software required More complicated file-level restoration Note: Because this solution replicates the whole virtual machine, file-level restoration is more complicated. Not aware of virtual machine state Note: Storage Replication has no awareness of the virtual machine state. As a result, data inconsistency is possible.

Manual Snapshots - XenCenter - XenServer includes disk snapshot capability for all SR types. You can use a GUI in XenCenter to quickly create a snapshot of a virtual machine for backup purposes. You should create manual snapshots prior to making server or virtual machine changes so that you can revert to a stable configuration if needed. 
Note: You can restore the virtual machine from XenCenter by creating a new virtual machine from the snapshot.

Benefits	Considerations
Fast and Easy Requires minimum storage space Integrated into XenCenter Can be performed when the virtual machine is online or offline	Manual, might not be suitable for large environments More complicated file-level restoration Note: Restoring files in this solution requires restoration of the full virtual machine and manual file retrieval after this.

Scripted Snapshots through XenAPI - You can make snapshots from either the XenServer command-line interface or through a XenServer API call. These snapshots can use the Citrix VSS provider for Windows virtual machines, which results in an application-consistent snapshot. You can also script these backups to occur automatically at predetermined times.

Benefits	Considerations
Fast Requires minimum storage space Integrated into XenCenter Customizable to specific business needs Virtual machine restore can be done from XenCenter Note: The snapshots appear in the virtual machine's snapshot list in XenCenter, simplifying full virtual machine restoration. Can be performed when the virtual machine is online or offline	Requires additional knowledge of comand-line interface or XenAPI More complicated file-level restoration Note: File-based restoration still requires the virtual machine to be restored and manual file retrieval.

Enhanced Backup Enablement with Third-Party Backup Products - XenServer allows you to combine snapshot functionality with a third-party backup solution. You benefit from the speed and size requirement of the XenServer snapshot functionality, while protecting investments in an existing third-party backup solution.

Benefits	Considerations
Fast Requires minimum storage space Optimized performance for virtual machines Protects investment in current backup solution, knowledge, and application-specific features Offers advanced backup functionality through third-party software	VSS-based approach available for Windows virtual machines only

For more information about integrating XenServer with third-party backup solutions, see Citrix article CTX122191