Citrix's Robert Hammersmith took me to task last week for pigeon-holing XenDesktop as just an old-school server-based computing product that connects to Windows XP or Vista hosts instead of Terminal Server hosts. Specifically, he wrote:
Brian frequently misses the boat when he talks about XenDesktop. In fact he recently assessed that XenDesktop is just an "old school server-based computing remote desktop delivery product". To even suggest that, one has to seriously sell the XenDesktop product short of what it really is. And I find that surprising coming from Brian, as he has been one of the biggest fans of the Ardence technology, which is a significant component of XenDesktop.
Robert is absolutely right. I am a huge fan of Provisioning Server.
And he's also right that I didn't know (or forgot?) that the license for Citrix Provisioning Server that's included with Citrix XenDesktop allows you to stream disk images to virtual machines and to physical machines. In other words, today's XenDesktop replaces the old Ardence Workstation Edition and gives you all the SBC / VDI XenDesktop features.
Is XenDesktop really more than VDI?
Robert wrote that XenDesktop was not just VDI. Instead, it's an entire "desktop delivery system." This is true if (1) you define VDI as server-based computing only and (2) if you don't want to support offline users.
(This is yet another reason why I'm using that "VDI+" term to apply to all forms of desktop virtualization, including offline / local hypervisors and streamed disk images to local clients. But that's not the point.)
The point is that while I thank Robert for pointing out that I mischaracterized Citrix XenDesktop, the reality is that XenDesktop is still limited to use cases where users have active network connections to servers. In the traditional VDI / SBC use, then the users are remoting their entire desktops via a remote display protocol such as ICA. And in the Citrix Provisioning Server / disk image streaming use case, the client device receiving the streamed image (be it a VM, remote blade, or physical PC) must have a constant connection with the Provisioning Server hosting the disk image.
So both use cases require a server. Period.
(Sure, Citrix says offline support in Provisioning Server is coming. Great! But they also say offline VM / VDI execution is coming, and VMware has beta code for offline VDI available to the public today. So yeah, all this offline is "coming," but it's coming from Citrix AND VMware AND probably Microsoft too.)
What's Provisioning Server's use case for VDI+ today?
I love love love love love love love Citrix Provisioning Server. As I've said again and again, every single environment in the world with more than two or three identical XenApp Server's should be running via Provisioning Server. And I love Provisioning Server for SBC-based VDI solutions. I think it's the perfect way to manage the disk images for a datacenter full of Windows XP or Vista VMs or blades.
But using Provisioning Server to stream disk images to physical PCs... oh boy... that's a tough thing to do in the real world. The problem is that in order to share a single disk image among multiple devices (which is the whole point of Provisioning Server in the context of VDI), all the hardware has to be identical. (Or very close to identical.) Sure, you could play with things like sysprep or "over build" you disk images with respect to device drivers, but the bottom line is that every different model of client device will have to be dealt with, and that's a huge headache (and the reason that most desktop-oriented Provisioning Server installations use blades or VMs, since each of those limits the number of different hardware profiles an admin would have to deal with).
So does Citrix XenDesktop have some huge advantage over the competition because it allows you to stream disk images to physical client devices? Is it really a "desktop delivery system" while the competition are "just" VDI? I don't know. I really don't. I think you'd have to deal with it on a case-by-case basis. Maybe if you were buying all new clients and you could ensure they were all the same make and model?
And then there's [the lack of] offline...
The big limiting factor, again, is going to be the offline use case. And who knows, by the time Citrix adds offline support to Provisioning Server, VMware might have made their offline VDI real? Heck, maybe they'll even have their client-based bare-metal hypervisor available? Of course maybe Citrix will have announced more by then too? Really we just have no idea, and this is one more reason I say that unless you have a very specific use case that could benefit from the server-based VDI today, stay away until these technologies mature a bit more.
The reality is that with both solutions today, offline use requires some form of Windows to be physically present on a client device. Whether that instance is managed or not is irrelevant, because at the end of the day, it has to be there. That will change at some point. But not today.