Category Archives: Xendesktop

The Elusive Windows “Companion Subscription License” – a Solution In Search of a Problem

In our post entitled “What Licenses Do I Need,” we discussed the licensing required, from both Citrix and Microsoft, for a XenApp or XenDesktop deployment. But there was still an unknown factor: When that post was published, Microsoft had recently announced something that, at the time, was being referred to as a “Companion Device License” – but no information was available yet on what it would cost or how it would be licensed.

The fog has finally cleared, and, unfortunately, it’s not particularly good news if you are a Small or Medium Enterprise.

The question at hand is what Microsoft licenses are required to legally operate a Virtual Desktop Infrastructure that serves up virtual instances of Windows 7 or Windows 8.x to your users. And the answer is that it depends on what the client device is that will be used to access the virtual desktop. If the client device is a Windows PC covered by Software Assurance, no problem – the right to access a virtual desktop instance is one of the benefits of Software Assurance. But if the client device is a Windows PC that is not covered by Software Assurance, or if it is not a Windows PC at all (e.g., Mac, Linux, thin client, etc.) then you must purchase a Virtual Desktop Access (“VDA”) license for that client device. That VDA license is available through Open Value Subscription licensing for roughly $100/year each.

So far, so good. But things start to get more complicated if you want to access that virtual desktop from a personally-owned client device.

According to the Microsoft Product Use Rights document (on pages 74 & 75 of the April, 2014, edition, in case you want to read along), the primary user of a Windows PC covered by Software Assurance, or of another client device to which a VDA license has been assigned, has “roaming use rights” that allow a virtual desktop to be accessed from a “Qualifying Third Party Device” such as a personal PC, MacBook, iPad, etc…”from anywhere off your or your affiliates’ premises.” And therein lies the problem: The user is not entitled to bring a personal device into the office and use it there to access a virtual desktop.

So, if your objective is to enable BYOD and let your people bring in whatever kind of device they want to use, and then use that device to access your virtual desktop infrastructure, what do you have to do? This question is what Microsoft attempted to address with what is now called a “Windows Companion Subscription License.” But it doesn’t address it very well. First of all, the Companion SL must be associated with another client device that is…yep, either a Windows PC with Software Assurance or some other client device that you’ve assigned a VDA license to. For every one of those you have, you can purchase a Companion SL, which will entitle the primary user of that device to access a virtual desktop from up to four Companion Devices in any given 90 day period. Therefore, the Companion SL doesn’t truly enable BYOD in the sense of eliminating the need to purchase company-owned client devices that are covered by either Software Assurance or a VDA license – because you have to have one of those before you can even purchase a Companion SL.

To make matters worse, unless your organization is large enough to have a Microsoft Enterprise, Select, or Select Plus agreement, you’re out of luck, because the Companion SL is not available through any Open License program. So, if you’re an SMB, your only option for legally licensing employee-owned devices for use on your premises to access your virtual desktop infrastructure is to purchase VDA licenses for those employee-owned devices.

If you do have an Enterprise or Select agreement, you can expect to pay an estimated $48 – $84 per year for a Companion SL, depending on your agreement, the size of your organization, and the concessions you’ve been able to wrangle out of your Microsoft account rep. So that may offer some cost savings for large enterprises that want to institute a BYOD policy – although it’s not clear to me how great the savings would be considering that you have to have a client device with either Software Assurance or a VDA license before you can even purchase the Companion SL.

For most organizations, in our opinion, the Companion SL is a solution in search of a problem.

What Licenses Do I Need….

Earlier this week, I had a long discussion with a client (you know who you are) about what licenses they would need for a deployment of “zero client” devices. We’ve written a lot about Microsoft and Citrix licensing, about XenDesktop and XenApp, about the Citrix trade-up, etc., but it occurred to me that it might be beneficial to pull all the licensing information together into one post instead of expecting you, gentle reader, to have to sort through multiple posts to pull it all together.

So, let’s discuss Citrix licensing first, then move on to the Microsoft licensing.

First of all, if all you want to do is to deploy VDI (Virtual Desktop Infrastructure), and you have a limited number of users, then you should probably purchase VDI-in-a-Box.

If you decide that VDI-in-a-Box is not the right fit foryou, the next question you need to answer is whether to use XenApp licenses or XenDesktop licenses. Beginning with the introduction of XenDesktop v4.0, Citrix concluded, reasonably enough, that an organization that was deploying VDI probably wouldn’t get much leverage from a concurrent-use licensing model, because their concurrency ratio (by which I mean the ratio of total users to concurrent users) would be pretty close to 1:1. So XenDesktop v4.0 was introduced with a per-named-user or per-device license model. These licenses were roughly half the cost of the comparable XenApp concurrent-use license: XenApp Enterprise Edition, for example, carries an MSRP of $450 per concurrent user. XenDesktop Enterprise Edition carries an MSRP of $225 per user/device.

At the same time, Citrix made the decision to include XenApp rights in the XenDesktop license. So if you buy XenApp, you get only XenApp. But if you buy XenDesktop, you get both XenDesktop and XenApp – so you can use XenApp to stream applications to your virtual desktops, or have your virtual desktops function as client devices that run published applications that execute on the XenApp servers, or simply deploy a mixture of XenDesktop and XenApp to your user community depending on what delivery method is best for a particular use case. This is what Citrix refers to as the “FlexCast” delivery model.

This created the interesting situation where, because of the difference in license cost, if your concurrency ratio was less than 2:1, you were better off financially to purchase XenDesktop licenses even if all you really wanted to run was XenApp. And, since delivering what Citrix calls “hosted shared” desktops from XenApp servers makes more efficient use of the underlying hardware and storage infrastructure, the bias should probably be toward XenApp unless there is a clear use case for why users need to connect to individual desktop OS instances rather than a shared XenApp desktop (and it isn’t just appearance, because with XenApp v6.5 on Windows Server 2008 R2 we can deliver a XenApp desktop that looks and feels like a Windows 7 desktop). But, for the sake of this discussion, let’s move on down the XenDesktop trail.

Citrix has re-introduced a concurrent-use license option for XenDesktop, which is a better choice for organizations who want to deploy both XenDesktop and XenApp, but have a concurrency ratio greater than 2:1, but so far, I haven’t seen very many use cases where that license model made sense.

If you already have XenApp licenses, and want the ability to deliver VDI as well, you can take advantage of the Citrix trade-up program to transform your XenApp licenses into XenDesktop licenses. And if you trade up all of your XenApp licenses, you can get two XenDesktop user/device licenses for each XenApp license. So 250 XenApp licenses would become 500 XenDesktop user/device licenses. If you want more information on how the trade-up program works, and what your trade-up options are, check out the handy Citrix Trade-Up Calculator.

As of the release of XenDesktop v5.0 Feature Release 1, the license service got pretty smart in terms of how it managed those user/device licenses. This is good news for, say, a hospital, which may have devices that are used by multiple users and other users who use multiple devices. The license server can intelligently and dynamically reassign licenses between users and devices to make the most efficient use of the available licenses. For example, consider the following scenario for a brand-new environment where no licenses have yet been assigned:

  • User 1 logs on from client Device 1. The license server will, by default, check out a license to User 1.
  • User 1 logs off, and User 2 logs on from the same client device. The license server, now sensing that two different users have logged on from the same device, will take the license that was assigned to User 1, and reassign it to Device 1. Any subsequent users who log in from Device 1 will not cause any action by the license server, because Device 1 is already licensed.
  • If User 1 logs on again from a different client device, the license server will again check out a license to User 1 (so, at this point, two licenses are checked out: one to Device 1 and one to User 1). Since User 1 has logged on from two different devices, the license will remain assigned to User 1 unless/until manually released by an administrator (e.g., in the case of the employee leaving the organization), or unless User 1 doesn’t log on for a period of 90 days, in which case it will be automatically released due to inactivity.
  • Likewise, since two different users have logged on from Device 1, that license will remain assigned to that device unless manually released or automatically released due to 90 days of inactivity.

So…how do you know how many licenses you really need? There is actually a formula that will tell you that. You need to know how many total users you have (let’s call that number “A”), how many shared devices you have (let’s call that “B”), and how many of your users will use only shared devices (let’s call that “C”). The formula is A – C + B. So, if you have 1,000 total users, 300 shared devices, and 600 of your users will use only shared devices, you need 1,000 – 600 + 300 = 700 total licenses.

For more information on exactly how this works, see the Citrix Community Blog post by Christophe Catesson, which in turn links to a recorded session from Synergy 2011 that was a deep dive discussion of XenDesktop licensing.

Now for the Microsoft licensing component.

If you have users who will be executing applications on a XenApp server, you will need a Remote Desktop Services (RDS) CAL for that user, or for the client device that user is using. It is very difficult to manage a mixture of user CALs and device CALs in a Remote Desktop Services environment, so, in most cases, you’re going to be better off purchasing user CALs.

If you have users who will be attaching to a virtual desktop instance, the licensing requirements are different, depending on the client device. If the client device is a Windows PC whose Operation System is covered by Software Assurance, you do not have to purchase any additional Microsoft license to use that PC to connect to a virtual desktop. If the client device is not a Windows PC, or that copy of Windows is not covered by Software Assurance, you need a Virtual Desktop Access (VDA) license for that client device. VDA licenses are only available under the Open Value Subscription license model at present, meaning that you will continue to pay for them every year. Forever.

But wait! That’s not all! As Gabe Knuth outlines in a recent article on, there is a very strange loophole in the VDA license terms. If you have a VDA license for your primary device (or if it’s covered by Software Assurance), you have what Microsoft calls “Extended Roaming Rights,” which allow you to also use your home computer to access your virtual desktop, or use your iPad when you’re at home or traveling. But, technically, it does not entitle you to bring your iPad into the office and use it there! To solve that (using the term “solve” loosely), Microsoft recently announced something called a “Companion Device License” (CDL) which allows you to use up to four other devices (in addition to the primary licensed device) to access your virtual desktop. No word yet on what the CDL will cost.

So let’s see if we can summarize what our client would need for a deployment of “zero client” devices (like, for example, the Wyse Xenith thin client).

  • You’re going to need some kind of Citrix license, either VDI-in-a-Box, XenDesktop, or XenApp.
  • Since the thin client is not a Windows PC, and therefore cannot be covered by Software Assurance, you would need to purchase a Microsoft VDA license for it.
  • If the thin client will be used only to attach to a virtual PC desktop and execute applications within that desktop OS environment, no additional Microsoft license is needed. However, if the thin client will also be used to attach to applications that are executing on a XenApp server – either directly or indirectly by having the Citrix client baked into the virtual PC desktop – you will also need a Microsoft RDS CAL.
  • You do not need an RDS CAL if you are only using XenApp to stream packaged applications to a virtual (or physical, for that matter) desktop for execution there. Since you are not actually utilizing Remote Desktop Services by executing code remotely on a Remote Desktop Server, no RDS CAL is required.
  • If you want to institute a BYOD program, where users can bring whatever client device they wish into the office and use it to access your VDI, you’ll probably need some of the new Microsoft CDL licenses.

If I’ve overlooked anything, feel free to submit questions via comments on this post, and we’ll try to get them answered. Let the discussion begin!

Best Practices for Provisioning XenDesktop

We’ve written a lot here regarding XenDesktop’s two provisioning methods: Provisioning Services and Machine Creation Services. Earlier this week, at the Citrix Synergy Conference in San Francisco, there was a session specifically devoted to discussing those two provisioning methods, providing a high level overview of how they worked, the best practices for deploying each of them, and even some guidelines for how to determine which approach is best for your organization. For the benefit of those who couldn’t make it to Synergy – or those who did make it, but would like a better way to share that information with others in their organizations – that session was recorded and is available on Citrix TV. You can view it below:

Beware of Vendor-Sponsored “Analysis” Reports

Mark Twain allegedly came up with the famous line: "Figures don’t lie, but liars figure." That’s a good thing to keep in mind any time you’re looking through a report that was sponsored ("sponsored" = "paid for") by a vendor that concludes that their product is better than the other guy’s.

Maybe it is better than the other guy’s. But you might want to look closely at what was tested, how it was tested, and whether they were, shall we say, selective in the facts they present.

Case in point: The Tolly Group’s report, released May 27, comparing VMware View 4.6 Premier Edition to Citrix XenDesktop 5 Platinum edition. There are several interesting aspects to this report, which are dealt with in detail in Tal Klein’s blog over on the Citrix Community blog site. Here are a few of the more egregious items:

  • VMware View 4.6 Premier licensing costs less than XenDesktop 5 Platinum. Absolutely true, and absolutely irrelevant. That’s like pointing out that if you load every possible dealer option onto your new car, it’s going to cost more than the basic model. Thank you, Captain Obvious. If you want an "apples-to-apples" comparison, you need to compare VMware View to the XenDesktop VDI Edition. But wait, if you do that, XenDesktop is actually less expensive, and that would be an awkward point to publish in a paper that’s being paid for by VMware.
  • VMware’s PCoIP provides a more consistent multi-media experience than XenDesktop 5. (Over a LAN. Using a single thin client device that did not support any of the Citrix HDX media acceleration features.) Sorry, guys, but once again this is not an apples-to-apples comparison. And did they publish any results of testing across a WAN link? Nope…and for the same reason they didn’t use XenDesktop VDI Edition for their price comparison.
  • It’s easier to upgrade View 4.5 to View 4.6 than it is to upgrade XenDesktop 4 to XenDesktop 5. Once again, both true and irrelevant. It’s easier to give your kitchen a new coat of paint than it is to rip out the cabinets and completely remodel it. Anybody surprised by that? There are significant architectural changes from XenDesktop 4 to XenDesktop 5. It shouldn’t be surprising to anyone that this will involve more effort than a "dot release" upgrade.

I’ve always been skeptical of vendor-sponsored "analysis" reports, and, to be fair, Citrix has used the Tolly Group in the past for its own sponsored reports – but it seems to me that this one is just over the top. Apparently, former Gartner analyst Simon Bramfitt agrees. His pithy assessment of the report: "There are undiscovered tribes lost in the darkest parts of the Amazon jungle that would know exactly what to do if a vendor airdropped a pile of competitive marketing literature authored by the Tolly Group; send it back, and asked [sic] that it be re-printed on more absorbent paper."

What do you think?

IntelliCache and the IOPS Problem

If you’ve been following this blog for any length of time, you know that we’ve written extensively about XenDesktop, and spent a lot of time on best practices and problems to avoid. And one of the biggest problems to avoid is poor storage design resulting in poor VDI performance.

In a nutshell, the problem is that a Windows desktop OS uses disk far differently than a Windows server OS. Thanks to the way Windows uses the swap file, disk writes outnumber disk reads by about 2 to 1. You can build your virtual desktop infrastructure on the latest and greatest server hardware, with tons of processing power and insanely huge amounts of RAM, but if all of the disk I/O for all of those virtual desktops is hitting your SAN, you’ve got a scalability problem on your hands.

Provisioning Services (“PVS”) can help to mitigate this in two ways (assuming for sake of argument that you’re provisioning multiple virtual systems from a common, read-only image): First, if you build your Provisioning Servers correctly, you should be able to serve up most of the OS read operations from the Provisioning Server’s own cache memory. Second, you can use the virtualization host’s local disk storage as the required “write cache” – because all of those write operations have to go somewhere while the virtual system is running.

But XenDesktop 5 introduced a new way to provision desktops called “Machine Creation Services” (“MCS”). We wrote about this in the April edition of our Moose Views newsletter, so if you’re not familiar with all the pros and cons of MCS vs. PVS, I’d encourage you to take a brief time out and read that article. Suffice it to say that, despite all the advantages of MCS, the biggest downside of using MCS to provision pooled desktops was that all of the IOPS hit your SAN storage, which limited the scalability of an MCS-provisioned VDI deployment.

But all of that just changed, with the release of XenDesktop 5 Service Pack 1, which was made available for download a week ago (May 13). With SP1, XenDesktop 5 is now able to take advantage of the “IntelliCache” feature that was introduced as part of XenServer v5.6 Service Pack 2. Using MCS with the combination of XenDesktop 5 SP1 and XenServer SP2…

  • The first time a virtual desktop is booted on a given XenServer, the boot image is cached on that XenServer’s local storage.
  • Subsequent virtual desktops booted on that same XenServer will boot and run from that locally cached image.
  • You can use the XenServer’s local storage for the write cache as well.

The bottom line is that you can move as much as 90% of the IOPS off of the SAN and onto local XenServer storage, removing nearly all of the scalability limitations from an MCS-provisioned environment.

With most of the IOPS for running VMs taking place on local storage, it’s pretty straightforward to figure out how many VMs you can expect to support on a given virtualization host. Dan Feller’s blog post does a great job of walking through the process of calculating the functional IOPS that your local XenServer storage repository should be able to support, and inferring from that number how many light, normal, or power users you should be able to support as a result.

This also means that using XenServer as the hypervisor for your XenDesktop 5 deployment is going to yield a significant performance advantage over any other hypervisor, unless or until the other guys come out with similar local caching features. So, if you’re a VMware shop, my advice is this: Go ahead and virtualize all of the supporting XenDesktop server components on your VSphere infrastructure. Run your XenDesktop 5 VMs on XenServer hosts, and just don’t tell anyone! If you’re asked, just say, “Oh, yeah, these are my XenDesktop host systems – they’re completely separate from our VSphere infrastructure, because we don’t need the (insert favorite VSphere feature) function for these systems.” Your infrastructure will run better, and no one will know but you…