| Modern servers are powerful beasts. They can spend much of their time waiting for work. Sometimes the limitations of what the Physical Server can do are more of a limitation of Windows server than of the Physical Box itself. As an example I’m looking at a SQL server which is monitored by our Kare system. Yesterday the CPU averaged 7% utilisation, at its peak it reached 50%. That tells me the CPU has room for more work. This Physical Server has 4GB of RAM installed, because that’s all that the RAM that Windows 2003 will see. But the Physical box will hold 30GB of RAM.
If this client now needed to add a Terminal Server to their network, they would normally need to purchase another server at around $8,000. But if we virtualised the current SQL server back on to the same hardware, we could add more RAM and some more disks for $2,000 then run both the SQL and the Terminal Server as guests on this one host. That would also save on power and space, and money! What is needed for Virtualisation?
The first question to be answered: Do I have a need for virtualisation? That is not one that I can answer here. If you have multiple servers or need multiple servers then virtualisation may reduce your hardware costs. Talk to us and we'll help you work it through.
You will need a physical server (host). This is not special hardware; we use the hardware that is likely to be supplied for a stand alone server. It will have more RAM and most likely more disks. The disk configuration also needs to be suitable for the work load of the server.
Virtualisation does require some special software. There are two main players in this space: VMware and Microsoft Hyper-V. License options and cost vary for different versions, starting at 'free' and going up from there with differing feature sets and licensing models. The one that best suits you will depend on your needs and the complexity of your network. It is a competitive space with a lot of innovation going on, and the normal product feature leap-frogging is very apparent.
Advantages of Virtualisation
As I have already mentioned above, virtualisation can reduce hardware costs, allowing you to leverage more value from the investments made. Virtualisation also simplifies replacing hardware. The guest servers are simply a set of files, which can be picked up and moved from one host to another. Because they can be moved, spreading the load of guests across more than one host is also simplified.
With shared storage (called a SAN) the licensed versions of both VMware and Microsoft Hyper-V will do some of that load-balancing on fly. With the correct versions and setup the system can automatically mount a guest from a failed host on to a running host.
Disadvantages of Virtualisation
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Up till version 4 of VMware, there was no way to directly monitor the health of the underlying hardware. Version 4 has opened up this reporting to the guest servers.
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Guests do not have access to some server resources. UPS monitoring is the most common issue here. Your UPS needs a network card so the Guest can shut down before the Host does.
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Virtualisation can not be used if your Guest requires access to serial ports. Although it is supported, experience tells us that it will most likely fail.
Things to be Aware of
The big thing to remember is disk space. If the Host runs out of disk space, all your Guests will go down. This is almost guaranteed to result in corruption. Proactive system monitoring, for example Kinetics KARE is a MUST.
Summary
Server Virtualisation has a place in most environments that require more than one server. Using it can reduce hardware cost and simplify future hardware upgrades.
Virtualisation is also used in single server sites. This can be used for a quick migration of an existing “software server” on to new hardware when the old hardware has reached end of life. The original software versions are retained and the configuration is simply moved to new hardware. (Some caution is required with this approach if the server is one that wold normally benefit from direct hardware access)
Virtualisation works. It’s an option and can save your business significant cost though lower hardware investments. Once virtualised, your network becomes more flexible and changes can be faster at lower labour costs.
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