Server Virtualization, Network Virtualization & Storage Virtualization Explained

There are many types of virtualization- server, network, storage, and more. In this article, we will demystify these complex terms, explain what they can do for you, and name specific products that provide these functions. So prepare for the smoke to be cleared…

What is Server Virtualization?

Out of all three of the different types of virtualization discussed in this article, I believe that server virtualization is the type of virtualization you are most familiar with. When people say “virtualization”, they are usually referring to server virtualization. However, they should really clarify what type of virtualization they are talking about because there are multiple types.

The Wikipedia defines virtualization as “a broad term that refers to the abstraction of computer resources”. Another definition, also from Wikipedia is “a technique for hiding the physical characteristics of computing resources from the way in which other systems, applications, or end users interact with those resources”.

With those definitions as our background, what is server virtualization? Simply put, server virtualization software allows you to run multiple guest computers on a single host computer with those guest computers believing they are running on their own hardware. By doing this, you gain all the benefits of any type of virtualization: portability of guest virtual machines, reduced operating costs, reduced administrative overhead, server consolidation, testing & training, disaster recovery benefits, and more.

Examples of server virtualization products are:

  • VMware Server, Workstation, Player, and ESX Server
  • Microsoft Virtual PC and Virtual Server
  • Xen
  • Virtual Iron
  • And more

That said, different products provide different levels of virtualization. There are:

  • full virtualization – guest OS is unmodified and believes it is running on the same hardware as the host OS
  • para virtualization – guest OS is modified, as with Xen
  • emulation – guest OS is unmodified but it is running on a software emulated CPU

There is no doubt that server virtualization is the wave of the future. Consider these facts:

  • A 2007 Forrester Research study found that 40% of businesses are using server virtualization. Of those 40%, 50% of those are using VMware products and 9% are using Microsoft.
  • Microsoft will be including Server Virtualization as part of the next release of the Windows Server operating system, codename Viridian.
  • Cisco has announced a strategic investment in VMware and Cisco has stated that they believe that virtualization (across the board) is the future of computing. Cisco has made virtualization part of their Data Center 3.0 strategy.
  • Microsoft will make the Windows Server 2008 virtualization software “Xen-Friendly

Here is what Server Virtualization looks like:

Server Virtualization Diagram

What is Network Virtualization?

When I first heard of network virtualization, I thought of VLANs. I thought, “don’t we already have network virtualization when we use VLANs?” I mean, a VLAN is a “virtual LAN”, which sounds like a virtual network to me. While this logic makes sense, there is much more to network virtualization than just VLANs.

Like these other forms of virtualization, network virtualization is not that new. Sun and HP have been talking about network virtualization for years. Now, Cisco has picked up the network virtualization ball and run with it. They are touting NV as the next big thing and as an integral part of their Data Center 3.0 strategy.

What does network virtualization do? The theory behind network virtualization is to take many of the of the traditional client/server based services and put them “on the network”. To Cisco, this means making routing and switches perform more services. Cisco says that the 3 parts of network virtualization are: access-control, path isolation, and service edge. This can be ambiguous when you first read about it but Cisco has a nice diagram that lays it all out to better visualize what it can do for you.  As you can see from the diagram, inside Cisco’s routers and switches you would find services like security, storage, VoIP, mobility, and application delivery. To Cisco, it is their strategy to continue generating revenue from their strong network infrastructure offerings. To me, this just helps to increase the value of your network devices and leverage the network infrastructure that is already required.

Another network vendor actually has, in my opinion, a stronger network virtualization initiative than Cisco. That company is 3Com. While 3Com is the equivalent of “David” to Cisco as “Goliath”, 3Com actually has a working card that is inserted into a router. On that card is a fully-functioning Linux server that has a connection to the backbone of the router. On that Linux server, you can install applications like packet sniffers, VoIP, Security applications, and many more. In the future, it is planned to be able to run VMware on that Linux card so that you could, conceivably, run Windows Servers. 3Com’s open-source network virtualization initiative is called 3Com ON, or open-network.

Network virtualization is still in its early stages and it is too soon to really say what it will or won’t do for IT Pros like you and I.

What is Storage Virtualization?

Recently, I attended a conference on storage virtualization. The main presenter was Datacore. They have some fascinating products but they aren’t the only storage virtualization products available. However, they may be one of the more reasonably priced.

So what is Storage Virtualization (SV)? Again, like network virtualization, when I first heard about storage virtualization, I thought that if I had a SAN, I was already doing it. However, like network virtualization, there is more to it than that. Wikipedia defines storage virtualization is “the abstraction at any layer in the storage software and hardware stack.”. This is what a SAN can do, in general, but there are many more features that SV can bring you.

Let’s look at an example. In most data centers, you only use a small percentage of your storage because, even with a SAN, you have to allocate a full disk LUN to the server (or servers) attaching to that LUN. Say that that LUN fills up but you have disk space available on another LUN. It is very difficult to take disk space away from one LUN and give it to another LUN. Plus, it is very difficult to mix and match storage and make it appear all as one. Storage virtualization works great for mirroring traffic across a WAN and for migrating LUNs from one disk array to another without downtime.. Additionally, you can perform thin-provisioning with SV where you can create new LUNs for new servers but you over allocate the disk space on the server, compared to what the SAN is really configured with. Say, for instance, the Windows server disk manager thinks that you have 500GB allocated but, really, you only allocated 1GB. While the utilization may grow to 6GB when Windows is installed, lets say that you never grow the server beyond that. You have just saved 494GB of disk space but you still have the flexibility to grow your data on that LUN without doing anything else.


In summary, the Virtualization creates “virtually” an unlimited number of possibilities for system administrators. The trouble with it, is being able to understand the different types of virtualization, what they offer, and how they an help you. To aid in your understanding, here is a quick summarization:

  • Server Virtualization = physical server hardware is separated from Guest opearting systems (servers), providing additional capabilities and benefits – think VMware
  • Network Virtualization = network applications are moved into the network devices, providing additional capabilities and benefits -think Cisco, 3Com ON
  • Storage Virtualization = disk storage complexityies are hidden from operating systems and additional capabilities and benefits – think Datacore

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