When it comes to server consolidation or building a development environment, virtualisation is at the forefront of making these efforts successful. A sound enterprise-grade virtualisation strategy includes careful planning. This includes appropriate selection of the components that will make up the virtualisation infrastructure beyond the host servers. A critical component to your strategy must include appropriate shared storage in order to take advantage of the high-end features of virtualisation software.
The type of storage you choose for virtualisation is dependent on your specific needs, as well as on the type of virtualisation you choose to use. For the purposes of this article, I'll be focusing on only two main types of virtualisation: host-based -- running your virtual machines under software that is installed on top of a host operating system, such as VMware Server or Virtual Server 2005; the second type is bare metal -- running VMware ESX Server, for example.
With both types of virtualisation, you can choose either host-based or shared storage, but you should be aware of some of the limitations imposed if you decide to stick with host-based storage rather than a SAN or supported NAS device. The host-based virtualisation software is not SAN-aware, but you can still run your virtual machines from a SAN or fast NAS unit by using the underlying operating system's SAN connectivity. You won't get the full benefits that you would get from running your virtual machines from a SAN, using bare-metal virtualisation, but it remains an option to consider. I'll go into more detail on each of these setups below.
Host-based virtualisation and host-based storage (host/host)
This scenario is the simplest to grasp and the easiest to
implement. Here, everything is local -- the virtualisation software, the virtual
machines, and the storage. Further, since the virtualisation software runs on
either Linux or Windows, you're probably already familiar with managing the
environment. However, in this scenario, your virtual machines are afforded very
little real-time protection.
If your host server dies, all of the virtual machines will go with it. Sure, you can back up the virtual machine files and restore them in the event of a failure, but the process will be somewhat time consuming and, depending on how you handle the backup, you may lose some data.
Host-based virtualisation and shared storage (host/shared)
If you have a SAN or a supported NAS device, and you want
host-based virtualisation (due to cost, perhaps), this is your best option. In
this scenario, the virtual machines still run on top of the host operating
system, but you can store the virtual machine configuration and data files on
the SAN. While the virtualisation software itself is not SAN-aware, you can
still take advantage of the capabilities offered by your SAN to keep your environment
more highly available. For example, using this method allows you to make use of
your SAN's snapshot capability meaning that, if a virtual machine is corrupted,
you can easily recover. Further, if your virtual host server dies, you can
fairly quickly mount the SAN volume on a different server and bring the virtual
machines back up.
Beware the storage virtualisation quick fix
One of the really hot areas of development in the storage world is virtualisation. One storage expert has clear ideas on the future, and in particular what he sees as a key mistake many companies are making with virtualisation. The lesson? Avoid the siren call of a low cost, easier-to-implement in-band virtualisation solution.
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Virtualisation 101
Systems programming has a new, hip word -- virtualisation. It has captured the hearts of IT professionals in small and large companies with its promise of freedom from the tyranny of hardware. We look at the different forms of virtualisation.
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Case study: City of Fontana
In early 2003, IT staff at the City of Fontana, California began seeking a centralised storage solution with virtualisation capabilities to standardise and support a new enterprise resource planning system. Goals for the solution: improved storage utilisation, reduced management complexity, and support for future growth.
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Case study: Lufthansa Systems
Lufthansa Systems has been planning and operating its data storage on a strategic basis with one of the most modern computer systems in Europe for years. By the end of 1999, the IT managers at Lufthansa Systems were certain that changing the storage system was the only possible and economically efficient way to manage its continuous and long-term data growth.
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Case study: Cuisines Schmidt
Cuisines Schmidt is the French leader in the manufacture of fitted kitchens and bathrooms. The existing Storage Area Network -- supplied by a leading storage vendor -- was at full capacity, did not allow systems to be restored quickly enough, and was not effectively disaster-proofed. Find out what the company did to overcome its problems.
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