Citrix XenServer is a commercial implementation of the open source Xen virtualization solution. Citrix has extended the base Xen engine with management tools and tightened up various components related to implementing and managing Windows and Linux virtual machines, not to mention integrating the whole shebang with the company's virtual desktop initiative, as well as its foundational server-based desktop and application delivery solutions.
Citrix XenServer is a solid server virtualization offering that installs easily, boasts good hypervisor performance, and includes enterprise capabilities such as load balancing and high availability. I did encounter a few snags with the management console and tripped over some issues with the overall solution. There is a lot to like about Citrix XenServer, but it isn't as polished as some of the other options.
Citrix XenServer installation
Citrix XenServer 5.6.1 installs as easily as VMware vSphere and Red Hat RHEV. Fire up a physical server with the install media, and within a few minutes you have a functional XenServer host. Like other Linux-based virtualization products, you can opt to install via PXE and pull the required packages in from HTTP, FTP, or NFS repositories. Plus, the ability to leverage automated installation scripts makes installing multiple hosts extremely simple and straightforward. Once the hosts are built, the Windows-based XenServer management console is installed and connected to one of the new hosts, and you're off and running.
Configuring the host is fairly simple, with the usual steps of identifying and configuring network trunks, locating the storage, and other general configuration tasks. In these tests, XenServer was able to leverage the Citrix StorageLink APIs that allow XenServer to configure the iSCSI SAN array itself. This is a bit of a double-edged sword, though, as it brings with it the benefits of copy and zero off-loading and other advanced features, but requires that each VM reside in a dedicated LUN on the array, rather than a large general LUN. With a large SAN and a good amount of VMs, the number of LUNs can grow exponentially, complicating otherwise simple management and administration tasks outside of XenServer. It would be nice to have the option of using dedicated LUNs or a general LUN, while still getting the advanced SAN features.