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This posting is provided "AS IS" with no warranties, and confers no rights. The opinions expressed within are my own and should not be attributed to any other Individual, Company or the one I work for. I just happen to be a classic techie who is passionate about getting things to work as they should do (and are sometimes advertised and marketed as being able to?) and when I can I drop notes here to help others falling in to the same traps that I have fallen in to. If this has helped then please pass it on - if you feel that I have commented in error or disagree then please feel free to discuss with me either publically or privately? Cheers, Dave

Thin Clients, VDI and Linux integration from the front lines.... Raw and sometimes unedited notes based on my experiences with VMware, Thin Clients, Linux etc.

So….  Question?

Would I use TS/Citrix or would I use VDI if I was building or designing the Front-Office of a Greenfield site today?

This is a quite a hot topic, because as much as VDI/xDI/DDI is the latest craze that’s sweeping the IT sector, is it really all it’s cracked up to be?

What has changed?

My thoughts are that until relatively recently Corporate IT was rock solid and unchangeable, absolutely rooted in Change Management, driving Mainframes and COBOL – but now we are living in a much faster paced world, whole countries and attitudes are shifting rapidly – and as a consequence Business’s need to respond to an ever faster changing world, it’s markets and it’s pressures – now IT not only NEEDS to be Agile and Flexible – it is paramount above all else (OK, well perhaps Security and Corporate Governance, did I hear Shareholders from the back row? mmm ;-) 

Anyway, Agility and Flexibility are the key here, in nearly every conversation I’ve had with C-level execs this comes through time and time again – IT needs to be in step with the business demands, not the other way around

And so with this in mind I can well understand the reasoning behind Brian Madden’s comment:

This VDI/xDI/VCC thing is hot. Even if you don’t believe in it today, the concept of delivering a desktop as a service is going to continue to grow. (In fact, many people are now realizing that some form of this might soon replace all desktops in a corporation—-not just the “special case” scenarios that are popular today.)

Why is it so popular? Well how about this example of quick provisioning:

When I have been to visit a client to initiate a PoC (Proof of Concept) that involves installing components on a Win32 Server and we quickly cover off the pre-requisites (indeed, sometimes this has already been done via email, just not actioned ;-) and I’m told “No problems, we have ESX in the lab, I’ll set it up from a template while we go and grab a coffee and it’ll be ready when we get back”

This sort of thing happens all the time these days, and yet it was unheard of say 3 – 4 years ago? Before the advent of ESX as a provisioning tool like this there would have been a delay of 4 – 6 weeks while the Server was agreed, funded, sourced, racked, cabled and powered, and yet now it can be done in 30 minutes, fantastic, absolutely wicked!!

When management get to start thinking that this same process can be applied to every new starter, and each employee can have a newly provisioned Desktop done in 30 minutes to be accessed by whatever you have to hand it starts to really make sense that maybe, just maybe, IT can start to actually be so much more credible and responsive to the Business? Whether or not it’s the answer to Agility and Flexibility remains to be seen, but this is a powerful example that gets people passionate and thinking about so many different ways to do things that previously were quite possibly unthinkable.

So what’s missing?

Well for the moment the main issues are:

  • What happens when Joe Bloggs tries to login and finds his Desktop isn’t up for some reason?
  • Ideally from a management perspective you do not want individual users tied to individual desktops?
  • It only makes sense to have the desktops turned off when not in use to save capacity and power? How can the user be connected to a virtual desktop that’s powered off (or doesn’t exist)?

So this is what I think all of the various VDI/xDI/DDI Broker’s are trying to achieve:
Being able to deliver a seamless and dynamic login to an appropriate virtual desktop (small, medium or large sir?) that is called in to being or booted on the fly, possibly based on a number of templates, so that the user is served up the correct amount of resources within their virtual desktop, and then when the user is done and wants to logoff all work is saved as needed and the virtual desktop is then either turned off or left in a standby or hibernation mode as required or determined by GPO’s?

NOTE: It is my understanding that this is the ultimate goal of Citrix Trinity Project so that it will be ICA to ICA for the Remote Client right through to the Xen Server EXS Server

Clearly there is a bit more to it than that, but by using “redirected folders” and “Flex Profiles” within the users profile you can have most of the data being saved to where it should go, and by using an OS Streaming system like Neoware’s Image Manager or Ardence you can save yourself quite a bit of disk space instead of having to support a whole SAN full (desktops hard drive x number of users = lots).

But why not use Citrix?

But surely this is the case with Terminal Server/Citrix as it stands today? All a user needs is a valid UserID and Password? When they login the session is created on the fly and when they logoff the session is gracefully closed and disposed of and the resources are handed back to the Server for reuse.

Regardless of how the user gets access (Citrix or VDI), they still need to be provisioned with an Active Directory User ID and password? All of the other normal provisioning needs to be carried out and with VDI the Desktop needs to be booted to be available? and yet any user can initiate a Terminal Server/Citrix session on-demand so surely that’s easier to deal with from an Admin’s point of view?

One of the problems (or at least the perception of a problem) is that the Terminal Server/Citrix approach is a shared service for multiple users, if the Server becomes unstable for any reason it will take 60 – 80 users down in one hit, so for this reason it needs to be robust and maintained under strict Change Management, where as with the VDI/xDI model this is not the case each user has their own clearly defined virtual Desktop resource that is independent of all others. 

Now I'm also going to bold enough at this point to suggest that there always seems to be a few issues or problems that tend to effect medium to large Citrix Server Farms, in fact I would go so far as to say that for most experienced Citrix Consultants working for Platinum resellers they could be spending as much as 60 – 70% of their time helping customers fix problems with badly designed, poorly maintained or poorly performing Server Farms.

It is very easy to get one or two Citrix Servers running well and behaving nicely as any Load Balanced pair should be, but after that things can get scary pretty quick, I have heard and seen Farms of 20 - 30 plus servers being replicated simply by swapping out the mirrored drive with no thought to NewSID, or the fact that the original servers Access Data Store has been replicated across all servers!!! (Anyway, I digress…)

Another performance fact/myth is that I have been basing my numbers on the amount of concurrent sessions that I know a DL360 G4/5 can support. I have in the past been lucky enough to build a PoC that was then tested to failure point using Mercury LoadRunner so I am quite comfortable with quoting 60 – 80 users per BL20p G2 having seen it be driven to 90 and 100 users before performance was significantly degraded – but when I stop and think about all the installations I have been asked to review it strikes me that most organizations are getting something like 30 – 40 users per server?

I would be very interested in people’s feedback on this number – because as you’ll see below this can tip the scales very dramatically one way or the other.

Costs (based on 5,000 users):

Let’s have a look at the costs associated with each approach shall we?

Greenfield Design Criteria for 5,000 Users:

Front-Office assumptions:
60% Task based workers suitable for Thin Clients             = 3000
30% Knowledge Workers suitable for VDI                         = 1500
5% Developers or similar suitable for PC’s                        = 250
5% Mobile Workers with Laptops                                    = 250

Of the mobile workers with Laptops I would think that 60% (or more) of these could be provided with Mobile Thin Clients
60% of 250 = 150 with Mobile Thin Clients and 40% of 250 = 100 with traditional Laptops

Please bear in mind that if you compare different Servers i.e DL585 for VDI and DL365 for Terminal Server/Citrix then it’s probably best to compare HW$ per User as opposed to traditional density comparisons of users per server.

I’m more than happy to receive any feedback or flames on how you feel these numbers are wrong, don’t forget “your mileage may vary”?  ;-)

VDI Example:
90% of users on VDI = 4500 Users.

Density based on fully loaded DL585 or equivalent = approx. 200 Users per Server at a cost of USD 400 per user excluding Desktop License   
(based on 128Gb RAM, quad AMD 8222SE Dual Core 3Ghz, 2 x 72Gb 15K000 Drives, 4Gb Fibre Connector and 4 x core VMware VI License = approx. 80K USD, leaving aside costs of SAN?)

The main issue at the moment is Microsoft’s approach to VDI Licensing for the Desktop – the minimum for this is Retail Vista (not OEM) regardless if you are going to use XP SP2 or Vista. That is off course unless you are lucky enough to have some other form of generous Licensing arrangement with Microsoft courtesy of an SA agreement that was done some time back before Microsoft realised that they wanted to restrict or charge more for Streaming or Virtualized Desktops?

I have heard rumours (and only rumours) that some large Govt. departments here in Australia actually have “per user” Desktop Licenses as part of their SA agreement with Microsoft – if that is indeed the case then they can start heading off and doing VDI today with no real worries – however, I would be carefully checking the wording AND the date at which the current agreement expires as I’m sure that when that SA agreement comes up for renewal there could be a little surprise waiting?

Terminal Server/Citrix Example:
60% of users on Terminal Server/Citrix = 3000
30% on VDI

Density based on fully loaded DL360 G5 or equivalent = approx. 80 Users per server at a cost of USD 212 per user excluding Citrix and TSCAL’s
(based on DL 360 G5 32Gb RAM, Dual Core Xeon 3Ghz, 2 x 72Gb 15K000 Drives and Windows 2003 Ent = approx. 17K USD)

Further benefits may be gained for little additional cost by using Windows Server 2003 for higher user densities

Cost of Citrix Licensing for 80 ConCurrentUsers (CCU) = USD 48K (based on Platinum retail, Ent. would drop this to 36K)

When this is added to the USD 17K for the server = Total of 65K for 80 Users and this equates to a cost of USD 812 per user (662 for Ent. Citrix) – however this is based on CCU and as such this can be aggregated to possibly only needing more like 60 – 70% of the full number of users, if we were to do this then this would bring the Citrix Licensing down to 28K. This brings the cost of 80 Users down to 562.5/user, but now I have to ask myself if I'm aggregating the licensing cost down to make it cheaper - should I still be thinking this Server calculation would be for 80 Users? Possibly, but now it's on a slippery slope?

Cost of Servers was calculated using HP’s US based web site as of 11/08/07

So on initial inspection we would appear to have:
VDI = USD 400 per user (exc. costs of Desktop License)
Citrix = USD 562 per user (exc. costs of TSCAL)

And to me this looks like it’s quite favourable to Citrix, when you add the cost of the Desktop License then the advantages of a Citrix deployment with it’s ease of use, readily available skills, mature product set and features, it’s almost a no-brainer?

However, as discussed above, if you change the figures to reflect that you can only achieve a max. of 40 users per server then it starts to tip the other way. Now we have a 17K server and 14K of Citrix Licensing only supporting 40 Users and the server cost per user now becomes USD 775.

Although VDI is currently “in vouge” I would have not thought that VDI can match the “Bang for the Buck” that can be achieved by Terminal Server/Citrix Installations, however I am now thinking that it's quite likely that other people's numbers won't neccessarily be the same as mine and this could be based on a wide number of factors. So this then may be very influential in peoples perceptions and may well have an impact on what the numbers are calculated to be in ROI’s and TCO’s before commencing a project.


As I was composing this I started to really appreciate that although to date Citrix and VMware have been quite amiable in their relations it could be that the impending acquisition of XenSource (thanks Brian) changes that forever and marks them as clear and direct competitors? Still it’s early days and there should always be some healthy competition? Citrix have always declared that “the Channel is in our blood/DNA” and they have a very healthy track record of taking new and innovative products to their existing customer base. 

For those that are contemplating looking hard at a VDI/xDI model now I would suggest that MS will keep the Desktop Licensing for Virtual and Streaming (VECD) pricing model very close to it's chest until Viridian is ready to be released, and then we could see a major lift in the take up of Virtualization for the Desktop.

And hopefully that should significantly add to the growth that IDC and others are forcasting for Thin Clients? ;-))

Posted on Tuesday, August 14, 2007 4:52 PM Citrix , Microsoft Tips , VMware and other Virtualization tools | Back to top

Comments on this post: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?

# re: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?
Requesting Gravatar...
Sorry, but why are you considering to use Citrix Presentation Server Platinum Editon? I think you should consider offering the same featues in both scenarios, and Platinum Edition give much more than a VDI implementation, like SSL VPN access, password management and end user monitoring, features that might even be not needed. I'm even wondering if you shouldn't calculate the Advanced Edition: on the other side, you are not quoting Virtual Center.

In the same way I feel that 200 virtual workstation on a DL585 is a very high number, while 80 citrix users on a DL360 G5 is reasonable for heavy users, but not for office users.

It is just my opinion, but numbers might get really different.


Left by Francesco Dipietromaria on Oct 02, 2007 1:57 AM

# re: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?
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Hi Francesco,

You are absolutely right, and I did include some calculations for the Enteprise edition - although it was more of an afterthought at the time, and I guess it might have been me being slightly biased towards trying to arrive at a solution that might have been more favouable to VDI than Citrix? my apologies.

As far as numbers go you feel that 200 is too high for the DL585?
And you think 80 users on a DL360 G5 is too low?
Left by Dave Caddick on Oct 02, 2007 5:52 AM

# re: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?
Requesting Gravatar...
I think it's very hard to compare those technology right now. VDI is becoming more and more interesting but right now there are several feature missing, or hard to implement (think about using scanners o usb pen) even if we know that these gaps will be close very soon (there are external hardware to mount usb pen, or think about usb 3). Citrix is investing lots of money in vitualization (Desktop Server and XenSource acquisition) and Mr. T is not crazy: the market is going that way. But I still think that today using Presentation Server is more convenient. I really hope citrix will boundle Desktop Server licenses inside Presentation Server Platinum, because beeing able to chose the right technology for the right user would be great.

Talking about the hardware, I never tryed to put 200 workstation on a quad- dual-core system. I managed to have 250 PS4.0 concurrent users on a 4x AMD opteron dual core w/ 32GB ram, but the system was quite stressed and I preferred to run it in production with 170 users because I wanted the system to be able to smoothly manage peak work.

Thank you for your reply, and my apologies for my previous post: I didn't ment to be aggressive.

Left by Francesco Dipietromaria on Oct 02, 2007 7:41 AM

# re: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?
Requesting Gravatar...
You are absolutely right, it is very hard to compare at the moment, and as far as Scanners and USB devices go **Watch this space** - I'm hoping to be able to highlight the HP solution that allows this to be resolved with Thin Clients shortly.

Citrix has more than a few options at this stage and their biggest problem will be how management and marketing decide how Desktop Server is to be priced, but I'm sure that will also have to be done in concert with their XenSource pricing?

When I switch over to my new blogging site at I'm hoping to set up a poll or survey regarding numbers of concurrent connections, we'll see how things progress? ;-)

Left by Dave Caddick on Oct 02, 2007 8:28 AM

# re: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?
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In regards to scanners, the 3rd party product Remote-scan ( has worked quite well for us. We use it with Terminal Server as well as Citrix (since the citrix twain redirection is problematic and unpredictable ), and we have heard that remote scan works with vmware , etc. The larger issues with comparing TS/CX with VDI has more to do with optimizations and management, but the the scanner part, just like printing in general, is taken care of by 3rd party apps.
Left by Gorden Honkle on Dec 16, 2007 5:36 AM

# re: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?
Requesting Gravatar...
Surely storage needs to be a huge factor in your comparison?
Your VHD's for the VDI solution take up a lot more space than a hybrid profile on WTS/Citrix, unless you deploy some fancy tool for streaming/differencing your VDI instances.

As for capacity/processor comparisons, I usually see same server capable of 2-3x users running WTS/Citrix versus multiple XP images. Scaling is different, but very much depends on applications. No problem putting 100+ office workers onto dual-socket Terminal server.
Left by Ian on Jan 11, 2008 11:39 AM

# re: Greenfield design - should you use Terminal Server/Citrix or VMware's VDI?
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Hi Ian,

I don't disagree - I have been using Neoware's Image Manager in the past to keep the storage way down (there's also Citrix's Ardence product) so to a certain extant if I were to look at serious VDI implementation of over 50 - 100 I'd be using that anyway - so I essentially didn't look too deep in to the storage side of things as this can be dealt with to a greater or lesser degree...

I think you are correct at this stage regarding the differences between them regarding users per core, however VDM2 now has the ability to suspend or power down inactive VDI's so that will start to improve things - but at the same token Citrix is still charging quite a premium while VMware is slowly coming under pressure from Citrix/Xen/Hyper-V, etc.

I think it still is very much a case of "horses for courses" depending on Customers existing Infrastructure, previous technology investment, etc...

Left by Dave Caddick on Jan 11, 2008 2:17 PM

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