Citrix XenServer is virtualisation software allowing multiple computers known as virtual machines to operate on a single computer by sharing resources.
XenServer provides a layer between the physical computer’s hardware and the multiple virtual machines hosted on it. Allowing the virtual machines to interact with the hardware indirectly through the XenServer software. This software intercepts calls to the hardware from the virtual machines and provides the appropriate resources such as processing power, memory, disk access to networking.
The hardware resources on the physical computer are shared with the virtual machines, with XenServer providing the control and monitoring to ensure, the virtual machines can operate effectively.
XenServer can host virtual machines running desktop operating systems such as Microsoft Windows 7 as well as server operating systems such as Microsoft Windows Server 2008 R2. Other operating systems including Linux derived systems can also be hosted.
The current version of XenServer is 6.1, released on 27th September 2012.
XenServer is available in four editions, the Express Edition, the Advanced Edition, the Enterprise Edition and the Platinum Edition.
The Express Edition is available for free but the other editions
are chargeable, these include the Advanced, Enterprise and Platinum editions. Each edition respectively from Advanced, to Enterprise, to Platinum provides additional features in relation to the edition which precedes it.
The XenServer Express Edition is available for free and is a cost free way to implement virtualisation. This Express edition does have less features than it’s chargeable siblings and is designed for smaller businesses who don’t need the advanced features available in the other editions.
The free version includes,
– XenCenter management console,
– Virtual machine conversion tool,
– Virtual machine disk snapshot and revert,
– Xenmotion live migration.
The advanced edition has the following additional features on top of those found in the Express Edition.
– automated VM protection and recovery,
– Live migration with Storage XenMotion,
– distributed virtual switching,
– high availability,
– memory optimization,
– performance alerting and reporting.
The Enterprise Edition has the following additional features on top of those found in the Advanced Edition.
– dynamic workload balancing,
– host power management,
– intellicache storage caching,
– live memory snapshot and revert,
– provisioning services (virtual),
– role based administration,
– storageLink storage features,
– web management console with delegated administration.
The Platinum edition is designed for complex environments where dynamic management of virtual machine workloads is required. The Platinum edition has the following additional features on top of those found in the Enterprise Edition.
– Provisioning services and Site recovery
– Site to site recovery
Licenses are assigned to each physical server which hosts virtual machines. The individual virtual machines do not require any licensing from XenServer, so a physical server hosting fifty virtual machines would only need a single XenServer license.
Competitors also charge a license fee dependent on the amount of memory and number of processors assigned to the virtual machines hosted. This memory (known as vRAM – virtual RAM) and processors (known as vCPU – virtual Central Processing Unit) does not incur any additional licensing cost with XenServer.
XenServer provides the hypervisor element of a Virtual Desktop Infrastructure (VDI) solution. Whereby XenDesktop software controls the provisioning (the creation of) of virtual machines on XenServer. Providing instruction to create virtual machines ‘on the fly’ to deal with demand from users.
In this VDI scenario, XenServer provides hosting for desktop operating systems such as Microsoft Windows 7. Wth XenDesktop providing the management capabilities.