So, what’s all this about then?

Last week we started our first XenDesktop Masterclass from the UK hosted by myself and Patrick Irwin from Product Marketing. I’m the technical guy (Systems Engineer in the UK) with too much enthusiasm for my own good and he’s the level headed one that tells me to hurry up. That’s our dynamic. Seriously

We’ve done a bunch of webinars before around over XenDesktop but as it’s just the opening slot in what will likely be a long season of sessions we had to keep it pretty broad with content. In future we’ll go a lot deeper into the specifics of various different components such as XenClient, Provisioning Services, Storage etc (all based on what YOU want to know about) but for this one it’s entry level into XenDesktop.

Part of the reason we’re doing this as a Masterclass rather than just a traditional webinar (you sit and listen and get what you’re given) we can open it up to questions and requests. To say that this final hour was a success is an understatement. The questions flooded in and despite seeing most of these before I got back to work after my holiday it’s actually been a good exercise for me finding the information you asked for.

So as promised here’s a write-up of the Q&A in no particular order.

Q. In a XenDesktop environment using Provisioning Services what do recommend for the VMs pagefile?

A. We recommend that this is placed on a local HD in the same way PVS write cache is. Have a look at this link here

Q. Do you have any sizing guides for user load and data centre requirements?

A. The enterprise design guide we put out a while ago has a lot of very deep information and was actually written by our own testing department in the UK.

The thing I like about it is that it’s not only XenDesktop but also based around ESX (pretty popular out there in the wild, so I hear) and NetApp (another popular product!). So it’s as impartial as we can be without not actually writing it…which wouldn’t be much help. For OIPS and boot storms there’s a great article and video written by Daniel Feller and can found at this link

Q. Do you still need to purchase a Microsoft OS licence per VM?

A. Yes, each OS still needs to be licensed for its use. How you do this is down to how you pay for your OS licences already but MS recently ditched VECD costs for their customers in SA

Q. Are there assessment tools available for customers looking to deploy any of these solutions and if so do they show scalability options as well?

A. There is a pre-built environment you can download to run on XenServer or Hyper-V from this link (mycitrix account required). This is only a small environment for proof of concepts but could scale up to some degree and has everything you need. If you’re looking to push it then I’d strongly suggest engaging a Citrix partner to get one built up with you. This will give you a better understanding of how it all fits together and more importantly give you chance to poke around and play with it from scratch. There is always XenDesktop Express too which is FREE and gives you the basics for 10 users.

Q. How would you handle applications with limited licenses and that may not work as streamed apps so need installing properly? A dedicated virtual desktop image per limited licensed application?

A. Lots of options here. The rule I use is if it takes me more time to build a streamed app package than it would be to complete a regular rollout I should look at other options. Just because the tool is there for a task doesn’t always mean you can use it. If an application will not stream then here’s what I tend to do:

  1. Is App-V available and have I tried it on that? We support App-V for XenApp and XenDesktop and to the end user all they see in an icon to click. Generally packaging apps lead to the same place but via different roads.
  2. Install the App on XenApp and publish it. This way you can maintain that separation from the VMs OS and use Provisioning Services to maintain a single image of any XenApp servers silo’d away for that task. You’re still dealing with a single image then.
  3. Use VM-based Apps. If you’re not familiar with this it’s a feature of XenDesktop and XenApp which allows you to publish applications that are actually running on a VM, not on XenApp. This is handy if you’ve got apps that MUST run on a client OS like Win XP or Win 7 but in this case it’s ideal if the app also can’t be streamed OR ran from XenApp in the traditional sense.
  4. Install the App in the base image. Last resort really as the OS should be totally separate but in some situations this is the only way to do it. If I get to this stage I make sure that I build a separate base image (vDisk) for the group of users needing that application. This way you can still control who has access to it, even though it’s on a gold image.

Q. Are streamed Apps usable offline?

A. Yes. All you need to do is install the offline plug in and tell the published app that you want it to work like that. You can even do things like set time bombs so apps can only work offline for so long without reconnecting back to the network. Handy for 3rd party contractors.

Q. Any thoughts on using Res PowerFuse with XenDesktop?

A. Not personally as I haven’t used it but I know a man who has

Q. Touching on AntiVirus being pushed out to one OS, for licensing, does that count as one AV license as well?

A. Same a the MS OS question really. If you have any application regardless if it’s Office, AV, Football Manager (God, I love that game), Quake3, you will need to be licensed for every user that uses it or VM that it runs from.

Q. Does the OS sitting on the VMs have to be MS OS? The reason I ask is that we are currently on PS4.5 and are paying MS Office licences on all thin clients on the basis that all our thin clients connect to a Citrix Win2003 server with MS Office installed. Quite a few users only use web apps, so could be presented with Linux.

A. A few customers have asked for Linux VM desktops but right now it’s not something we’re looking at right now. From the sound of it if you’re already using PS4.5 and are deploying Office using that then you’re already doing things in the right way for your environment. The licenses you are paying for Office should really equal the CCUs you have for your PS4.5 farm. Add a comment if I’m getting the wrong end of the stick on this one…

Q. Can you take advantage of memory overcommit?

A. If your chosen hypervisor has it we can use it, whatever feature it is. XenDesktop (and myself) don’t really mind what you’re using underneath so long as it does the job for you. There is a one train of thought that says using memory overcommit in a VDI environment is as useful as an ashtray on a motorbike but that’s another discussion all together!

Q. How many vCPUs can be given to a VM?

A. It depends on your hypervisor again. We don’t care and will take what you have, XenServer using up to 8 per VM. I give W7 2 and XP 1 but in theory you could load it up with as many as possible. It does depend on how the OS understand and uses then and W7 is obviously a lot better at this than WinXP. I’ll see if I can dig out any testing results but if anyone out there has already done this feel free to chime in.

Q. How can you cope with CAD applications?

A. Even back in the old PS days we’ve been doing CAD applications and things like AutoCAD run on regular VMs and even shared desktops on XenApp. However if you’re looking to give virtual desktops to guys and gals who design oil rigs then it’s likely that your needs will go beyond what current hypervisors can offer. For this we suggest using physical blade PCs (event regular desktops) that are sat in your datacenter but used as virtual desktops. These can have nVidia graphics cards and be loaded with RAM and CPUs just right for the task of playing Unreal Tournament over a WAN…or actual work if you must These could even run from a single vDisk using Provisioning Services.

Q. Is there a best practice on how to cope with extension management when using Open Office and MS Office across the organisation? like XLS and DOC or so?

A. The best thing to do, assuming you’re using it, is to use let the Citrix Receiver handing the file extensions for apps that are being delivered via XenApp. If you’re pushing out Office then clicking on a .doc will then call that app to be streamed in. The OS will deal with anything else like .ini or .txt etc. The main thing to keep in mind is that the end users needs to be none the wiser. All they do is click and work.

Q. Hi, all looks good but have a question – how will VDI work with accessibility software?

A. This falls into two areas, screen scraping and dictation for actions. With ScreenScraping it’s pretty hard to do as in my limited experience most of the applications out there that do this by inserting their own display driver into the mix. This doesn’t seem to play nicely with the VDA we install to delivery the screen to the end client. I’m open to other experiences though. For mics and dictation this is pretty well covered in XenDesktop and XenApp because we support USB redirection for microphones and headsets so in theory (test first, of course) an application would just need to be installed into the VM to take those voice commands and away you go. I might see if I can get hold of an eval of Dragon and see how well it works. The app for the iPad is outstanding so I have high hopes!

Q. Speaking of AV shouldn’t it be enough to just have a streamed AV client running in memory and just scan the profile area and don’t give a damn about the OS (which is read-only anyway)

A. Spot on. This is the approach I take too. In a PVS environment the base OS is clean as a whistle and ideally should only need to pick up a new definition on boot or tackle scanning new processes happening during the session. When it’s logged off it gets wiped leaving a clean image. There are other considerations for AV such as where you put your definitions (local HD) so they are always persistent etc but we can touch on that in another session. There is another line which says there is no point using AV in VDI because it’s clean by design.

Q. In XD 4 are there any Role-based access controls for delegation of administrative duties?

A. Yes this was introduced in SP1 for XenDesktop 4. XenApp has always had this feature.

Q. How would you deal with hundreds of concurrent logons during logon peak hours?

P. The logons aren’t really the main problem here but getting the VMs booted up and ready. The IOps hit on a logon is roughly 14 while booting the VM is actually more like 25 to 30. We can negate the boot ups by managing an Idle Pool meaning we can tell all the VMs we need ready at 9am to boot up an hour or so before so they are ready to be used. We can also stagger how many boot up at once to take the load off your backend. NetApp PAM cards can also help with this and we have some things in the pipeline too

Q. With the single instance OS. If the root OS image gets corrupted or a virus, does this mean suddenly all the pooled desktops using that master resource will also suffer the same fate?

A. Only if it’s had that from when it was built but of course it’ll be tested and signed off in a state where you want your users to start working with it, right? The base image is always read only so any virus outbreak will not be committed to that base image. If one VM did get a virus you could just reboot that VM and it’s cleaned right away. The other part of this discussion is a virus outbreak spreading all over the shop. This should be treated in the same way it’s always been by putting the scanning engine on each VM. We could stop any virus outbreak by just rebooting the VMs but that might be bit too much of a hassle for the end users. Either way works, it just depends on what lengths you want to go to to prevent or clean up the mess afterwards.

Q. Is there used some local chache for User profiles? So if user was logged to that machine previously, it will be loaded faster?

A. Not as such but with Citrix Profile Manager we can choose to stream in the user profile as it’s needed rather than copying down the whole thing all at once. This will then mean quicker logon times for the end users so they can spend more time on Facebook

Q. Is there a client image optimisation guide for Windows 7 and Windows XP?

A. Oh yes, lots of them! For Windows 7 look no further than Paul Wilson’s blog particularly. For Windows XP Paul has some more tips but I quite like this post from Pierre at

Q. What about the combination XenDesktop and VMWare Vsphere?

A. Works very well with XD and 50% of my POCs are done using it. All it is to me though is a place to run a VM, power it up and shut it down. All the features it’s got like HA and Memory wizardry will work just fine but if you get a hypervisor FOR FREE and that’s got all the features you need then it does make sense to look at it.

Q. Is there a maximum of VM’s that can be run off one OS image?

A. The testing we’ve done using a physical PVS server was 3312 VMs from one PVS server. From a single OS image there are limiting factors which are mainly around the SAN (IOps) where the vDisk sits on as that’s where the vDisk is actually being read from. I’ll see if I can find out but I would say multiples of the single PVS server figure.

Q. What are the practicalities of using client devices to access xendesktop VM’s over 802.11n wifi. Would app streaming be the preferred method for WLAN devices such as ipads, and VDI for LAN connected clients?

A. WiFi isn’t an issue as ICA (the protocol you use to connect to the VM) is very thin. If you were to stream apps into the VMs that would actually happen in the datacentre so wouldn’t affect the WiFi. If you were going to stream apps over WiFi that again shouldn’t be a problem but I always suggest pre-streaming apps into any laptops where possible then only the changes will actually end up going out to the end users. It’s still a file transfer to a degree so you’ll need to treat it as such.

Q. Is it possible to use HDX to stream OS over WAN, or this should go trough VM on XenDesktop.

A. In theory so long as the WAN is lightning fast with LAN like latency then you could use PVS over a WAN but it’s much easier and kinder on all the other traffic to use HDX and just connect to the VMs remotely rather than locally streaming them. This also means you can get to the VMs from anywhere on any device rather than just from the desktop that happens to be on your desk in the office.

Q. Doesn’t XenApp published desktop offer the same functionality as XenDesktop?

A. Yes and this is at the core of FlexCast. To the end user they’ll just plug in a device like a webcam and it’ll work whether they’re on a Hosted XenApp Desktop or a VM based desktop. The difference is the stuff in the background like HOW that webcam is used. For example we use DirectShow to do it on XenApp and USB redirection on a VM. It comes down to what users need which execution environment for what their job entails.

Q. Hi, We have an evaluation environment of XenDesktop; how do I add XenApp into XenDesktop to deliver apps?

A. I’d recommend downloading the XenApp Eval kit but the XenDesktop one mentioned earlier has that built into it as well.

Q. Please explain how printing will work from a machine that is trying to print over the network and to a device connected physically to the machine?

A. Printing on a VM is done by going File->Print OK, maybe that’s a bit of a simplification but what we actually do is map the locally attached printer and pass that into the VM so when the user does press print it’ll go to that local printer, so long as that’s their default. If it’s a network printer it’s achieved using the same principle. The only thing to think about is printer drivers. We ship a universal printer driver that works well but some customers insist on using original OEM drivers which is fine, but it’s always better to at least attempt to standardise your printers while you do it.

Q. In the webinar I keep loosing the audio stream. is it just me?

A. It co ld wel be y ur own sys ems but VOIP is supported in XenDesktop and works really well so you might try that.

Q. Do you have to change the hostname from the template on each client? or does the client get a unique hostname?

A. Nope, Provisioning Services takes care of the VM name in AD so they all act as individuals as far as the OS goes. While this is great you do have to consider how this affects the apps/services running on it. Some AV needs to have registry entries removed before the vDisk is put into production so the apps/services also know they are unique. Generally it’s the same rules as you’d do in a Sys Prep image back in the good old days.

Q. Can it (the device you’re connecting from) even be a PDA device?

A. iPhone, iPad, Android, Blackberry Linux tablet, Windows Tablet… All supported with their own Citrix Receiver.

Q. Is there any degradation in the range of the USB rocket launcher when used via XENDESKTOP?

A. If you store the VM on a solid state disk SAN and use XenServer for the hypervisor you should be able to clear 30 feet on a 45 degree elevation. Previous tests have shown ESX could only manage 19 feet with vSphere only giving 22 feet.

Thanks very much for all those who attended and especially for the guys who stayed on for the Q&A. Remember to fill in the feedback form that was emailed to you and see you again soon for the next one



Systems Engineer
Citrix Systems UK