VMware OnDemand streaming technology will challenge Citrix’s Ardence platform

VMware presented a feature called "VMware OnDemand" streaming technology. This technology will allow a VM player to prefetch disk blocks from a disk image file across a network, allowing the VM to boot from that disk image before the image is 100% copied to the player machine.

Details are very light at this point, but during one of the keynotes at VMworld this past week, VMware presented a feature called “VMware OnDemand” streaming technology. This technology will allow a VM player to prefetch disk blocks from a disk image file across a network, allowing the VM to boot from that disk image before the image is 100% copied to the player machine.

This is VERY similar—at least in concept—to Citrix’s Ardence OS streaming technology. This can be huge in the virtualized desktop / VDI environment since it means that a user could start using a local desktop VM without having to wait for a multi-gigabyte disk image file to copy to their client device.

[Quick side note: Why would you want to run a “VDI” locally instead of centrally? A central VDI desktop means that you connect to that desktop via a remote display protocol such as RDP or ICA. This is essentially a “single user server-based computing (SBC) environment,” and with it you get all the advantages and disadvantages of SBC. Running a desktop VM locally has its own set of advantages and disadvantages. Therefore whether your desktop VM runs centrally or locally depends on your specific use case. For more information about this, check out the ten-page paper I wrote about it last year.]

Anyway, if VMware gets this “OnDemand streaming” thing right, they will have two major advantages over Citrix’s current Ardence OS streaming platform:

Advantage 1: VMware disk images run in VMs, not on native hardware

Ardence only virtualizes disk images. Once the image is streamed to the device (or as it’s being streamed to the device), it acts like a standard local hard drive. This can be a good thing. (Native performance anyone?) But it can also be a drawback. Imagine that you have 1000 PCs in your company and you want to give them all a standard disk image. Using Ardence you can configure them to all mount the same image every time they boot up. This is huge in terms of being able to “fix” broken computers (just reboot them) and being able to swap which images are used by which computers. The only problem is that there’s a good chance that all your desktops are NOT 100% identical. They have different motherboards and graphics cards and peripherals. They might even be different brands altogether. So what are the chances you can get away with a single disk image for all of them? Probably zero.

If you were in charge of streaming a single image to 1000 PCs, the ultimate fantasy (besides one in which all your users disappear) would be that the PCs were 100% identical. But this isn’t realistic. To mitigate this, Ardence has created some tools that let you add multiple driver sets to a single image so that image can be used on different client platforms. While this is definitely cool, it’s still not as easy as having 1000 identical PCs.

But what if there were a way to make all 1000 PCs appear to be the same hardware to the OS? ;)

Of course this is where VMware comes in. Since the VMware OnDemand will stream a virtual disk image to a VM player on a client, you can use the exact same disk image file on any client device.

Advantage 2: VMware disk images intrinsically run locally (read: offline)

Ardence does NOT work offline. The client device receiving the streamed OS must maintain fast network connectivity to the file server hosting the vDisk file (Ardence’s virtual disk format). In VMware’s case, the player architecture has grown up around offline use. The “offline” feature is already built-in.

This means that you can have a single disk image (or a single “desktop”) that can be used by all users—online and offline.

How will Citrix respond?

Ardence has been “working on” an offline solution since the earliest days that I talked to them over 18 months ago. Can we expect it any time soon? Who knows? Even if Ardence did release offline support, they’d still have to figure out a slick way to run the same image on different types of client PCs. And with this week’s VHD announcement, for all we know they’ll need to port their vDisk file format over to that ASAP.

Maybe this is where the XenSource thing comes in? Maybe Citrix is planning to use a Xen hypervisor-based solution to "offline enable" Ardence? Certainly that’s the way that VMware is doing it now.

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It is definately an interesting development. But to be honest i dont care what the name on the VDI components is going to be, just hope they will get a few products a bit mainstream targeted so the decision makers can relax a bit and make a decision instead of waiting to see how things touch down :-)


Is it not possible to cache Ardence image for offline use in laptops? VMware has to get rid of the host OS (below VM Player) if they are going to get any sense to this concept.
That is correct. You cannot cache the Ardence image at this time.

Both solutions have something going for them. Ardence can boot on bare metal which eliminates the need for an OS on the machine to which to stream, but is does not allow for precaching. VMware needs an OS to run the player (at a minimum some graphic shell) which requires the same infrastructure you already have to deploy. So for VDI on this solution is nice. Most VDI will be used on wired workstations in my opinion, so Ardence would be great. When one of the two gets the solution to do a precachable streaming OS which only needs a small VM (which should be embedded in the device) that will be the killer. Really when they allow the streams to be provided over the internet, updates all the time, everywhere.

I think we will see this solution within 6 months.

Best regards,
Marcel de Haas 

You can use Ardence to boot a VM too.  I don't see the advantage of VMware,  in this case Ardence wins because I can choose which hypervisor I want to use.

Brian,  You simply missed the point of advantage 1 as Ardence can stream the OS to a virtual machine,  not just HW.

Advantage 2 may not be that much of an advantage.  You'll need to stream 4-8 gigs each time the image changes.  Not mention an extra OS license and management tools for the host machine.



We all enjoy your forum here to learn about new technologies and how it applies to the rapidly changing world of Hardware, OS and application virtualization. I was very disappointed with the post. VM made what seems to possibly be a big announcement and there was very little explanation of what the technology does or how it compares. Take your comments above. You made it sound like Ardence only does  physical. Ardence has always streamed to virtual machines, just the same as physical. So I don't see the big difference. But, the real key to Ardence has always been streaming many to one. Thus negating the need for large SANs in a virtual environment. There are many other items here to discuss, but without a basis from you, we don't know what this new announcement from VM is. Is it competition to Ardence? Is it different? Are they complementary? Is it robust enough to compete with a 5 year old product?


OS streaming is rapidly becoming a strategic product at large customers. You have been a proponent that has helped fuel this. Please help us understand better the dynamics of these announcements.

I agree that one of the main reasons for blogging is to express opinion and to start a discussion...and it is working. I do agree with some of the comments regarding your post. I think it's to early to talk about "challenging" and "having the upper hand". And you give the reason for that yourself: "Details are very light at this point"

I hope we will see a more substantial justification of your statements soon.


I would like to take the time to add onto this comment.  Brian... have you physically tested this new feature or are you basing your article on marketing slicks and a presentation?  Why not test it and put a solid logical comparison together.  Heck... you still need a base OS to run VMWare player on top of.  Ardence can stream the physical and virtual machines.  Streaming Ardence into VMWare Player could prove a very powerful combination.  I know you are a huge fan of VMWare and Ardence, so you cannot be really accused of being biased.  This article seems a little off tilt and I would like to see more technical details.

Couldn't you do this already today with VMware?  Use VMware Player, keep the disks on some sort of NAS and run them all in non-persistent mode?  The NAS device/host OS essentially does the streaming then, no?  And the non-persistent disk functions pretty close to how I understand Ardence works.
We do this today with Wyse WSM. We create 1MB VM's and use Wyse WSM to stream the OS into the VM! It will be interesting to hear if this is actual VM's technology or the licensed this from Wyse or Ardence.
What will really make this all interesting is once an embedded hypervisor is released for desktops such as ESX 3i embedded on standard off the shelf desktops or Xensource's new embedded hypervisor. Then it would be very realistic to have a single image for all desktops whether it is streamed to a desktop or streamed to a server. I imagine this will become a reality in 18 to 36 months.

Even the boys at Provision Networks are doing this... "Image Virtualization"





The quality of information and insight you provide is usually very good. This one is a bit misguided and I can excuse that perhaps to enthusiasm and rushing. This is not a well thought out comparision, Ardence is designed to stream the OS efficiently regardless of host target whether is be hardware server, hardware desktop or virtual machine player. VMware is talking about loading a virtual machine file over the network with the ability to run without the full file transfer. It does not stream the OS to target devices, it transfers it to an existing OS that is running VMware software.


Also, Ardence does have features and tools to load onto different hardware targets to address difference in drivers and it does have a feature to load and cahce the OS on the local hard drive if you choose. For some reason it was there and then not available in the last released version, but my understanding is that it will be in the next version again.

"Ardence does NOT work offline.".....Actually yes it does. They have always been able to push out vDisks to client hard drives. It's simply not documented in the 4.1 release.

I have been streaming OS's to Vm's for a while now. Amazing how a 60kb set of files (Vm configuration files and vmdk) can be used to stream a desktop to a VM player - remember you don't actually need the hard drive.
How do you know that Ardence has offline mode? Have you tested it? Have you seen it working? I would like to try this. However, it sounds like vaporware?


You'll find a dedicated site explaining advantage of OS Streaming below :