XenServer 6.5 giving credence to Citrix's Hypervisor as key for Enterprise

XenServer 6.5 was released during Citrix summit. Not quite revolutionary enough to be a full new release, and obviously we can't talk about the monkey squirrel incident that involved versions 6.3 and 6.4. Still, a new version of a hypervisor that drives majority of number of Gartner magic quadrant mentioned IaaS clouds, and likely your XenDesktop or XenApp estate?

When it was released, I thought XenServer 6.2 had its benefits. I've used that release extensively. Mind, as we moved through 2014 and into 2015 it was apparent the XenServer 6.5 release had a number of jobs to do:

  • Address the calamity of messaging and confidence that 6.2's "open source" play did towards the viability of the hypervisor in the enterprise.
  • Resolve the poorly explained reasoning for removing a number of enterprise features: specifically Workload Balancing. 
  • Accommodate the growing demand for XenServer to deliver virtualised desktops with visually rich interactive graphics.
  • Provide a platform that could offer a more robust and powerful offering to competition from Microsoft (2012R2) and VMware (5.5, 6.0).
  • Never, ever, ever mention the Monkey Squirrel Incident. 

So what is new with XenServer 6.5? How does it compare to 6.2, and what has ceased to be? Most importantly, what does the XenServer 6.5 release do for existing, and prospective customers?


Citrix XenServer 6.5 - Updates?

As I've asked before of XenServer releases, how does the latest release embrace the Olympian ideal of faster, higher, stronger?  

Citrix XenServer 6.5 - Updated Client support

New and improved guest support for XenServer 6.5.0 includes:

  • Ubuntu 14.04
  • SLES 11 SP3 and SLES 12
  • CentOS 5.10, 5.11, 6.5, and 7.0
  • RedHat 5.10, 5.11, 6.5, and 7.0
  • Oracle Linux 5.10, 5.11, 6.5, and 7.0
  • Oracle UEK 6.x

the following Linux distros can run in HVM mode:  

  • RHEL 7.0
  • CentOS 7.0
  • Oracle Linux 7.0
  • Ubuntu 14.04

There is undoubtedly a growing demand for Linux desktops access, especially in Europe, where the maturity of Linux desktop provision offers a viable, and lower cost, alternative to Microsoft. Hence, an increasing and improved support for Linux distros: likely a driver for Citrix's introduction of the Linux VDA

XenServer 6.5 Licensing

XenServer 6.5 heralds the return of the format where licensing introduces additional features. With XS6.5 you can continue to run in an "unlicensed" state; however, you will not have access to all possible features, and you will not be eligible for direct Citrix Support.

Licensing is determined on a cost per processor. There are two "standalone" editions, Standard and Enterprise. When first released, there was an additional two licenses depending on your XenApp/XenDesktop license level (enterprise or platinum) but looking at the documentation the explicit Desktop/Desktop+ licenses have been simplified into In-Memory Read caching only being available for Platinum XenApp/XenDesktop license holders.  

This means there appears to be four (4) versions of XenServer available (more on that later). The following table gives a comparison of features between 6.2 (with paid support) in comparison to the 6.5 options:   











with Platinum XA/XD

64-bit Xen Hypervisor          
64-bit Dom0          
Active Directory Integration          
Role based administration and auditing          
Multi-Server Management with XenCenter GUI          
Live VM Migration with XenMotion          
Dynamic Memory Control          
Host Failure Protection with High Availability          
Performance Reporting and Alerting          
Mixed Resource Pools with CPU Masking          
GPU Pass-through for Desktop Graphics (AMD,NVIDIA)          
Intellicache for XenDesktop Storage Optimisation          
Live Memory Virtual Machine Snapshot and Revert          
OpenFlow capable distributed virtual switch          
VMware vSphere to XenServer Conversion Utilities          
Support for Intel TXT          
Hotfix Deployment Using XenCenter          
GPU Virtualisation (vGPU) with NVIDIA GRID          
Dynamic Workload Balancing & Audit Reporting Retired         
Export Pool Resoure List  New in 6.5        
In-memory Read Caching  New in 6.5        
Support & Maintenance          

Nice to see that the faff on deploying updates in the free versions has been removed by simply allowing complete integration with the new XenCenter.

Arguable that removing the conversion tool and support for Intel TXT support from the Standard edition is going to cause a problem. v6.2 Premium is more or less going to map to v6.5 Standard edition: yet, for many shops, XenServer drives their XenDesktop and XenApp farms, so they will likely pop in around the Desktop/Desktop+ editions where this feature is available.

That said, in a modern, security conscious world removing a function intended to improve security seems unnecessarily mean: hopefully room for growth in 7.0  

Anyhoo, for more information on Citrix XenServer 6.5.0 licensing - read the XenServer 6.5.0 Licensing FAQ. Be interested to hear your thoughts on that. 

XenCenter & APIs

Has had a makeover - if you ignored the buggy appeals to download the "newer" version of XenCenter the 6.5 version is a bit of a mindset change. More options to view information, which is good but at the expense (IMO) of it being a slightly less intuitive than the previous version. I had a couple of issues with the way process has changed in SR disconnection but other than that no major issue and finding where progress indication got hidden. Bear in mind if you've added extensions you may need to update your code as mentioned in the release notes

XenSever 6.5 API wise, I'm impressed with XenServer's per host HTTP interface has now been exposed in the PowerShell SDK, enabling users to perform operations such as VM importing and exporting, patch upload, retrieval of performance statistics, look forward to playing with that as when I've done automated deployment scripting having to set up UNC paths is tedious. And the XenAPI reference is now shipped within the SDK. 



XenServer 6.5 - Not your father's scaling?

While the last couple of releases of XenServer have seen steady scalability improvements, to continue the trend was going to stretch the capabilities of the underlying architecture. Modern, more scalable hardware has far greater potential than XenServer appeared to exploit: ask those who were trying to drive 10Gb networking performance for example, or drive fast boot times from multiple desktop instances.

To continue to be viable in the enterprise, XenServer needed to be better able to scale, and not only in numbers of virtual machines, but also in being able to handle that volume of VMs’ IO - be that storage or networking. 

What Citrix have delivered XenServer 6.5 included:

  • In-memory Read Caching - read caching improves a VM’sdisk performance as, after the initial read from external disk, all data is cached within the XenServer host's memory
  • Support for Tapdisk3 - the latest Dom0 disk backend design can deliver major improvements in the performance of concurrent disk access and a much larger total aggregate disk throughput for the VBDs when using modern disks. 
  • Network Improvements including but not limited to
    • Generic Receive Offload (GRO) being enabled by default for all compatible PIFs available to Dom0 which, if you've a GRO enabled NIC and you're pushing past 10Gb you should notice reduced CPU cycles and better performance. By all means shout up yeah or nay. 
    • Netback Thread per VIF  in XenServer 6.2 there was a fairness problem (gags on a postcard please) when processing network data for many VIFs which meant worst case, you'd be in a position where networking was restricted. In XenServer 6.5  each VIF has its own Dom0 netback thread that can run on any Dom0 vCPU. Thus less of a fairness problem and improved performance.  Bearing in mind that NetScaler implementations run on XenServer - networking improvements for scale and performance are key. 

At a high level, how does this actually stack up as a difference between Citrix XenServer 6.1 and Citrix XenServer 6.2?

Capability XenServer(6.1.0) XenServer(6.2.0) XenServer(6.5.0)
Virtual Machine Limits      
Virtual CPUs per VM 16 16

32 (Linux) 

16 (Windows)

Memory RAM per VM 128GB 128GB 192GB
Virtual Disk Images (VDI) (including CD-ROM) per Virtual Machine 7 7 16
Virtual CD-ROM drives per Virtual Machine 1 1 1
Virtual Disk Size (NFS) 2TB minus 4MB 2TB minus 4MB 2TB minus 4MB
Virtual Disk Size (LVM) 2TB minus 4MB 2TB minus 4MB 2TB minus 4MB
Virtual NICs per Virtual Machine 7 7 7
XenServer Host      
Logical processors per host 160 160 160
Virtual CPUs per host 900 4000 (Windows VMs) / 12000 Linux (VMs) 4000 (Windows VMs) / 12000 Linux (VMs)
Concurrent protected VMs per host with HA enabled 60 500 500
Concurrent VMs per host 150 500 (Windows VMs) / 650 Linux (VMs) 500 (Windows VMs) / 650 Linux (VMs)
RAM per host 1TB 1TB 1TB
Concurrent active virtual discs per host 512 512 2048
Physical NICs per host 16 16 16
Physical NICs per network bond 4 4 4
Virtual NICs per host 512 512 512
VLANs per host 800 800 800
VLANs per physical NIC #### 1019 1019
GPUs Per Host 4 12 12
Paths to a LUN  8 8 8
Multipathed LUNs per host  150 150 256
Multipathed LUNs per host (used by storage repositories) ####  75 256
VMs per SR 600  600 600
Resource Pool Limits      
Hosts per resource pool 16 16 16

You can find the reference documents and notes for these figures in the  Configuration Limits documents here XenServer 6.1, XenServer 6.2, and XenServer 6.5


Retired Features:

The XenServer 6.5.0 release notes don't mention anything specifically (exceptions between versions already mentioned) - but by all means check again.


Unretired Features - The WorkLoad Balancing Boys are Back in Town

XenServer 6.5 sees the welcome return of the WorkLoad Balancing (WLB) virtual appliance. WLB gives system administrators automated insight into system performance, allowing infrastructure optimization. WLB allows you to generate granular performance monitoring reports, alert administrators to system hot spots, automatically place workloads based on historic data, and dynamically moves workloads based on current CPU, storage and network load.

The enhanced Pool Audit Trail feature allows you to specify the granularity of the audit log report. Customers can also search and filter the audit trail logs by specific users, objects, and by time.

I've not tested it yet, but there is apparently an Online Upgrade feature that allows customers to apply upgrades directly from the live SLB Server by the yum update mechanism, or instead download the upgraded RPM packages from citrix.com.



So do you really get huge performance increases/fixes?

I have seen graphs that say so. I didn't: for me it was about 5-10%. That said, my lab h/w isn't exactly "cutting edge". One of the reasons I use XenServer is it tends to be more accepting of older hardware, is low maintenance and low cost in comparison to other hypervisors: be simple so I can concentrate on getting the day job done. When I get access to some updated h/w I'll post results.

As is with all things - test in your environment. ymmv.  Still, 3-4 year old kit got an increase with a software update - imagine what newer kit could do. Some have already been improvements - fellow CTP Dane Young for example talked about XenServer 6.5 Dynamic Memory and NVIDIA GRID vGPU? Now Fixed in 6.5! Go For It! 


Citrix XenServer 6.5.0 - Enterprise ready with a warp .5 engine?

XenServer 6.5.0 offers increased VM density, vGPU and storage performance - key for implementing your VDI. Increased networking performance - key for hosting Netscaler and pretty much anything else.    

Like a questionable daytime-TV script, XenServer 6.5.0 has righted some wrongs. Well done to the product management team for recognising this: by all means read In Search of Stupidity: Over 20 Years of High-Tech Marketing Disasters for prime examples of when this hasn't happened in IT. Still, many have struggled with previous versions of XenServer at scale so lets see whether the extra effort in testing and feedback brought in for 6.2 can convince those who are considering rediscovering XenServer to re-adopt.

For 6.2, I thought perhaps it had been accepted XenServer wouldn't match vSphere (too embedded) or Hyper-V (too readily seen as "free", and soon to be embedded). For many, both VMware and Microsoft are being seen to be expensive to manage - sheer per processor cost price and free management should make XenServer cheaper: which is likely why its popular to to host their CloudPlatform suite. There needs to be a schmooze fest to bring enterprises who left, back round. 

Despite my liking 6.2 even I recognised a difficulty for Citrix would be in choosing to play the "opensource" card: which did indeed turn off many enterprises. The "we offer a paid support version" fell by the wayside under the clamour of corporate perception of the ills of open source. This is being solved by many versions and different models to give that warm fuzzy feeling that some demand. I'd like to see three versions - free, standard enterprise - where standard and enterprise map to Desktop and Desktop+ - if anything it means if new features are introduced those features can only go in so many buckets which is better for the customer and easier to sell. 

Citrix still strive for that end-to-end capability that delivers hybrid cloud services. The marketing focus appears to have changed from 6.2 askew to enterprise mobility (XenMobile) to block based hardware allowing hyperscale of services. You can't have mobility without service support - how does that service support start and grow? Yet, hyperscale offering needs to be hosted on something. While  the hypervisor market is increasingly commoditised, if Citrix can better highlight an enterprise focused hypervisor that continues to support the latest hardware - they are better in control of their own, and their partners, destiny to build appliances that deliver building-block focused, meshed, scalable services.   

Interestingly, with the Atlantis Computing announcement XenServer 6.5 gives a platform for a wider range of appliances not only for networking but for storage. You can extend that to that hyper-converged services. Potentially XenServer's latest buff physique could push VDI-in-a-box to greater scale; it'd be interesting to see where Citrix partners with vendors to take on the likes of VMware's EVO:Rail   

When 6.5 was released I was one of many who suggested that it, given the dom-0 change it should be v7 with the practically ever responsive David Cottingham's response "this is more than a minor release, but not a radical change".

Changing dom0, re-defining the capability of scale, a significant XenCenter change. Faster, higher,  stronger, and absolutely no mention of monkey squirrels; I think the team have sold themselves short.

If this is what you get in a minor release - what of 7?