Innovative’s Brian Holzer on the new XenSever 6.5, aka “Lazarus”

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It seems that all of the latest hypervisor news has been focused on the stalwart VMware vSphere, or the new “contender” – Hyper-V on Microsoft Server 2012 R2. Most of my colleagues and customers had written off Citrix XenServer as a viable platform. In fact, rumors were rampant that, after releasing XenServer 6.2 as open source, Citrix was acknowledging defeat and would soon cease any development of the product at all.

It appears that XenServer 6.5, code named Creedence while under development at Citrix, should possibly have been named Lazarus, as it is returning from the dead. In XenServer 6.5, there are architectural updates, new features, re-introduced features, as well as performance improvements. The marketing people apparently got involved as well. There are new pricing and packaging options now as well.

What’s New

One of the most notable architectural changes is that dom0 (the control domain) now utilizes CentOS 5.10, and as a result is finally 64-bit. This change eliminates the restrictive memory division of a 32-bit system, which accommodates more PCI devices and memory.

Now that dom0 is a 64-bit system, it provides the ability to store read-cache data in RAM. This feature, known as in-memory read cache, dramatically improves I/O rates for hypervisor guests. This allows IT administrators to process a larger I/O volume without upgrading the external storage device(s) (SAN, NAS, etc.). In the end, this results in more I/O throughput, faster boots, etc., from the same exact hardware, resulting in happier users of the end user systems.

This latest release of XenServer incorporates the Project Xen 4.4 hypervisor. This hypervisor release allows for more event channels. XenDesktop installations benefit from this substantially, as desktop virtualization typically includes a high volume of virtual disks, network adapters, etc. This new hypervisor version also touts improvements in virtual disk and network I/O.

There are several storage improvements in XenServer 6.5. Of these, two alleviate common irritations of XenServer administrators. These two features are the ability for XenServer to free up previously used blocks from a LUN (i.e. deleted VMs from an SR) and live LUN expansion.

XenServer has been a market leader in supporting virtualized graphics processors. Some competing products feature GPU passthrough, but it was never a scalable solution for large volumes of desktop virtualization users. Approximately one year ago, Citrix introduced vGPU. Coupling this technology with NVIDIA GRID vGPU cards introduced realistic numbers of users could utilize higher end graphics in a XenDesktop session. Going a step further, XenServer 6.5 now includes support for 96 concurrent GRID vGPU sessions per host (a 50% bump from previous limitations).

Finally, one last noticeable new feature is support for additional guest operating systems. The newly supported guests include CentOS, Oracle, Redhat, SLES and Ubuntu.

What’s Back

Some administrators may remember workload balancing. Its presence was short lived, and it disappeared, along with some other features, as XenServer moved to open source. It’s now back, allowing guests to once again “float” between hosts in your XenServer pool as load dictates the need.

Citrix XenCenter has a new look and feel. Some may notice (unlike SCVMM) it keeps looking more like vCenter, allowing administrators who have managed a vSphere environment to easily transition to managing XenServers.

Marketing Re-swizzle

Of course, this wouldn’t be a true Citrix release without the marketing people getting in their two cents. I am almost surprised they didn’t decide to rebrand the product as part of the effort to gain/regain market share. CloudServer has a nice ring, don’t you think? It would be a simple extension to go a step further and rename XenApp, XenDesktop, XenMobile and yes, even NetScaler – CloudApp, CloudDesktop, CloudMobile and CloudScaler (They already have CloudBridge and CloudPlatform.) . It only makes sense because everything is about the cloud today. Okay, back from my tangent to XenServer 6.5.

With this new release, there are now two commercial editions of XenServer – meaning they are actually available for purchase. In addition to XenServer Standard Edition, there is now an Enterprise Edition as well. Both editions are licensed on a per-CPU socket basis (of the host) on either an on-premise subscription (a 1 or 3 year term), or as a perpetual license.

Just to make things confusing, Citrix added two XenServer entitlements as well. Both XenDesktop and XenApp include licensing for XenServer Desktop Edition. XenDesktop or XenApp Platinum Edition, include getting bumped up to licenses for XenServer Desktop+ Edition.

XenServer Standard essentially is the same as the free edition, with Citrix support added.

XenServer Enterprise, Desktop and Desktop+ Editions all add to that dynamic workload balancing, GPU Virtualization (vGPU) with NVIDIA GRID and VMware vSphere to XenServer Conversion utilities.

XenServer Enterprise and Desktop+ Editions also adds in-memory read caching.


With these changes, it’s still not as feature rich as vSphere, and the 3rd party tools are somewhat scarce, but XenServer 6.5 may just be a real contender to be the virtualization platform in your business. Couple these enhancements with the fact that you need not purchase XenCenter separately, (unlike vCenter and SCVMM), implementing XenDesktop using XenServer 6.5 is even more attractive. It packs quite a punch for a fairly low cost.

There are more features and more fine details about licensing, etc., on the Citrix web site. You can always contact your Citrix partner for more details. If you don’t already have a relationship with a Citrix partner, or you want a second opinion, feel free to contact me directly.

Brian E. Holzer, CCE-V, CCP-N, CCP-M, CCA-N (former CCI)
Sr. Architect
Innovative Integration, Inc.

About Tony Johnson

Innovative helps you balance your business requirements, service levels, staff and infrastructure to make your IT as effective as possible. Tony Johnson is Vice President of Operations at Innovative and has been helping clients optimize their IT spend and operations since 1983.

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