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.