XenServer Enterprise and Platinum allow admins to create load-balanced resource pools of Xen hosts. Shared storage repositories allow for live migration--XenMotioning in Citrix-speak, versus VMware's VMotioning--where running VMs can shift from host to host as production needs or operating requirements change.
XenCenter balances virtual machines across all available hosts based on processor and memory resources, and it assigns newly created VMs as needed. VMs may use a single host's local storage, but a "local" VM would need to be powered down and manually relocated to switch hosts.
XenServer will run on older hardware lacking virtualization support (e.g., pre-Intel VT or AMD-V chipsets), but you won't be able to run Windows VM guests, nor can you join the host to a Windows-aware resource pool.
XenServer's storage integration and management reveal a touch of elegance: Recognizing that customers have paid good money for advanced storage features, XenServer capitalizes on hardware-assisted snapshots, cloning, and replication options from a number of vendors.
Storage Delivery Services works with NetApp and EqualLogic arrays, integrating with vendor APIs to perform cloning and to take snapshots of virtual disks using the arrays' native feature sets. This reduces host CPU loads and decreases the time required for disk-intensive maintenance.
One of the most significant enhancements in this revision is the bundled automated high-availability feature, with which XenCenter can dynamically reallocate running VMs in the event of a host failure. Once high availability has been configured for a pool of XenServers, the group can absorb host failures with minimal downtime for running VMs. Setup is straightforward. If a high-availability-enabled host goes down because of hardware failure, power outage, or other error, XenCenter will assess current resource availability across the remaining host server pool and restart orphaned VMs.
Citrix also integrates XenCenter and high availability. While the management console resides on a primary Xen host, the latest version utilizes a distributed architecture so that any host in a resource pool can grab the management baton and keep running. We really appreciated the distributed nature of the management console. High availability wasn't instantaneous in tests, but the minimal outage window and ease of use will make it a winner for many installations.
And there shouldn't be much quibbling over the price. An Express version of XenServer is free, although it's limited to single host server management via XenCenter and doesn't provide resource pools or migration capabilities.
The $780 XenServer Standard allows multiserver management. XenServer Enterprise, which we tested, offers live migration, host resource, and storage at $2,600. XenServer Platinum adds dynamic workload provisioning of physical and virtual servers and requires an Enterprise license, plus licensing for Citrix Provisioning Server, for an additional $2,000.
Citrix's Subscription Advantage support plan costs extra.
We'll evaluate each vendor's ease of setup, configuration, and data and network connectivity. Each vendor's physical-to-virtual conversion tools will be used to migrate real-world servers running Windows Server 2000, Windows Server 2003, Windows Server 2008, Windows XP, and Debian Linux into the virtual world. We'll clone instances of the resulting VMs to generate up to 10 guest servers per host at maximum load. We'll assess loads for differing hardware resources within a single vendor platform and compare like tests across different hosting environments. Finally, we'll evaluate bundled management tools for ease of use and functionality.