To some IT departments, virtualization is at the server level, running multiple operating systems on one server. To others, it enters at the network level, consolidating multiple servers, managed from one logical entity. Still others apply it at the application level, keeping applications isolated from each other while operating on the same environment.

Regardless of how virtualization is used, it can impact the way organizations run their business, and will likely grow in the coming years. According to research firm IDC, spending on virtualization software and services is expected to exceed $15 billion worldwide by 2011, up from $6.5 billion in 2006.

A number of key considerations and challenges exist with virtualized server environments that IT managers should understand. Enterprise requirements, for example, in terms of application availability, performance and protection, are not addressed by virtualization solutions.

Mission-critical applications should be fully available, regardless of the underlying infrastructure. Though software-based high-availability capabilities are integrated into many

server virtualization solutions, they suffer from several deficiencies:

* Typically, availability is monitored at the virtual machine level. Action is taken only when a server or a virtual machine fails, but not when there is a failure of the OS or application software running on top of the virtual machine. Failure in the network connection to the server plus may not be detected.

* Since all server virtualization solutions are software-based, they monitor availability by implementing a software agent on each physical server, thus consuming resources of every server in the virtual infrastructure for that purpose only.

* Failure recovery date is typically as faraway as it takes to start a virtual machine on a different server. that may vary based on the machine load and can, in some cases, take up to several minutes. During that period, service is denied to citizens who were using applications…

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