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XenServer management for the VMware administrator

With the world of server virtualization changing at a lightning pace, folks who were once dedicated to VMware administration find themselves with new responsibilities. It’s becoming more common

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for VMware administrators to be responsible for Citrix XenServer management as well.

You could write an entire book on cross-administration between VMware and XenServer. (The platforms use two different architectures.) But there are a few main points concerning XenServer management that a VMware administrator should understand.

VMware administrators should realize the benefits of learning XenServer management. Having the expertise to administrate other hypervisors is a huge career development move for VMware administrators; today, increasingly more employers seek IT pros who aren’t limited to single-product specialization. Exploring XenServer also allows a VMware administrator to better understand the core fundamentals of hypervisor technology itself, and not just one vendor’s implementation of it.

To realize these benefits, a VMware administrator must be willing to learn about the underlying core technology of these Type 1 hypervisors, the differences in terminology and how to perform common tasks with the respective administration tools.

VMware vs. XenServer management: GUI vs. CLI
XenServer was not originally a Citrix product, but instead an open source Linux project, so XenServer management can be done through the command line interface (CLI). I once saw a Citrix engineer perform an entire multi-host implementation of XenServer from scratch, using only a terminal command line on his CentOS laptop.

Many VMware administrators are accustomed to the vCenter graphical user interface (GUI) and may never have touched a command line, so the CLI for XenServer management may require adjustment. A GUI management client called XenClient can help ease the pain.

Ironically, XenServer started out with a CLI for management and added a GUI, whereas VMware started out with a GUI and has since added more control via the CLI (PowerCLI and the vSphere Management Assistant). It all sort of comes full circle, doesn’t it?

How XenServer management works
VMware administrators will notice a few differences when working with XenCenter for XenServer management. XenCenter is a client software that you install on any machine on your network, for XenServer configuration and administration. The interface is basic compared with VMware vCenter’s, and the connectivity and design differ. VCenter has numerous capabilities for fine-tuning the environment, but with XenClient, you can barely change resources on a host.

XenServer’s hypervisor is based on domO, and its architecture is a distributed model rather than a centralized one. Thus when you open XenClient, it wants to connect to a host, not to a central server as VMware does with vCenter. You can specify any host in the “server pool” (think “cluster” in vCenter). Each host knows about the others, and one XenServer in the pool serves as the “pool master” -- which manages all commands given to that pool. The pool master role can be transferred to any host within that pool. This means you have to add all server pools to the client rather than having them all presented at once (think “data center” in vCenter).

Note that XenServer’s interpretation of pools isn’t the same as VMware’s. You have resource or server pools in XenClient, but they do not behave the same way as resource pools in vCenter. The same goes for resource scheduling and high availability. These XenServer management features are simply checkboxes in XenClient, but vCenter has options galore. Still, you can unlock many more options in XenServer by using the CLI instead of XenClient.

For the VMware administrator, another major difference with XenServer management is storage. XenServer uses storage repositories, whereas vCenter uses data stores. A storage repository that’s assigned to one server pool cannot be used by another server pool. With VMware, however, that’s not the case, and it can limit migration capabilities. One advantage to XenServer’s storage method, however, is that storage repositories come in several different forms.

If you’re a VMware administrator who wants to practice XenServer management, set up a test environment and shake the trees to get a feel for it. Believe it or not, you can even run XenServer inside of VMware Workstation or ESX as a virtual machine.

About the expert
Mike Nelson has been in IT for more than 20 years, with exposure to a very diverse field of technologies and solutions. He has devoted more than half a decade to virtualization and server-based computing. Currently, Nelson is a senior analyst at a Fortune 100 company in the U.S. Midwest.

This was first published in February 2011

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