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We have been recently looking into VDI solutions for prospects. And with the VMWorld 2008 session of Brian Madden VDI vs Terminal Services in our mind, we were at first a bit hesitant.
Especially when it comes to end-user acceptance and the remote display protocols involved. RDP, ICA / HDX, HP RGS (http://h20331.www2.hp.com/Hpsub/cache/286504-0-0-225-121.html), they all have their limitations. (Yes, we have demanding end-users:)

Since we do a lot a of VMWare and Citrix we looked at both VDI products. VMware relies for 100% on a remote display protocols but Citrix has bought Ardence which now has been rebranded into Citrix Provisioning Server.
Ardence / Citrix Provisioning Server is able to stream a full-blown OS over the network to physical and virtual machines. It actually mounts a disk over the network.

Check the video below for a very cool demo

Ardence Demo

So with Ardence all the limits of remote display protocols are gone for demanding applications.

Next to this all VDI vendors are fighting for the best remote display protocols. Microsoft bought Calista, VMWare Teradici (www.teradici.com) and Citrix is extending the ICA Virtual Channels with all kinds of nifty extensions like Flash HDX (Still techpreview) and 3D rendering using GPU’s at the server side. We did a PoC with Flash HDX which offloads flash rendering to the client and this rocks, although still beta with some quirks. Finally full quality Flash on XenDesktop and XenApp. Another nice feature of XenDesktop is that it supports smartcards from the endpoint device

What’s new in FP1 of Xendesktop 3:
http://www.citrix.com/English/ps2/products/subfeature.asp?contentID=1686118

How does the Citrix VDI solution work?

It is actually based on a bunch of existing (proven) technologies:

- Ardence OS Streaming
- Application hosting / streaming from XenApp
- ICA into a client OS (XP / Vista / Window 7), sort of single user Citrix box.

VDI into the Physical Standardized Desktop

OS Streaming on the LAN based on Citrix Provisioning Server (rebranded from Ardence). Citrix Provisioning server streams a single disk image over the LAN to multiple desktops which then are able to run a full-blown OS without the limitations of remote display protocols and leveraging local computing power. By default the streamed disk image is non persistent and the OS on the desktop will return to the initial state after a reboot. When required dedicated, read-write images can be provisioned, however this breaks the single image storage advantage.

The application are then delivered onto the desktop using (“traditional”) XenApp either streaming or hosted.

And all personal settings are stored in a traditional roaming profile, profile management however will be necessary to keep al the bloat out. This can be done using Citrix Profile manager which comes with XenDesktop or your favorite profile manager.

VDI into a virtual Infrastructure

The same happens applies when you want to run Virtual Desktops in Virtual Infrastructue like XEN, VMWare or Hyper-V (All supported by XenDesktop). Not sure when vSphere 4 will be supported. The main difference is that you’ll need to access the Virtual Desktop using ICA/HDX and all the limitations involved. But the major limitation of flash over ICA is due to be solved with Flash HDX, which rocks. You’ll need to see this for yourselves, it’s 100% like running Flash locally.

XenDesktop 3 Architecture

Check www.brianmadden.com on all the pro/cons of the different VDI solutions.