Citrix Essentials™ for XenServer™ extends advanced server virtualization management capabilities to Citrix XenServer environments to help customers create highly scalable, manageable and agile virtual infrastructures. The solution supports the IT administrator throughout the application delivery lifecycle enabling optimized usage of computing resources through intelligent workload placement and rapid provisioning of new resources on demand. It also streamlines storage management in virtual environments with simple backup and maintenance through integration with existing storage platforms.
Citrix Essentials for XenServer is a product that must be purchased. Unlike XenServer itself, Citrix Essentials is not free. If you are going to have multiple XenServers you will probably want Essentials, but it is not required. Key features available with Essentials include dynamic workload balancing and high availabilty. High availability is a feature which will restart a virtual machine on a new host in the event the physical server it was running on goes down.
Suggested pricing for Citrix Essentials starts at $2,500 per server, regardless of the number of processors.