Although server virtualisation has quickly evolved into one of the most talked-about strategies for any self-respecting data centre manager, storage virtualisation needs to be embraced just as warmly to ensure the full benefits of virtualisation can be realised across the data centre, advises Andy Hardy, managing director of international sales at Compellent

Server virtualisation, which enables several applications to run independently on a single physical server, is an important first step toward achieving a virtualised environment.

However, server virtualisation is just half the story.  Data centre managers need to combine server virtualisation with storage virtualisation in order to achieve the full benefits that are available to them. 

The fundamental technique for consolidating IT resources is virtualisation. Virtualisation creates a pool of servers, storage, and other infrastructure resources that applications can share. Because applications in a virtualised environment draw from the resource pool without specifying the type of processor, memory, or storage required, the IT department gains the flexibility to choose the best underlying components.

Meanwhile, the availability of new tools to manage virtualised infrastructures can enhance the reliability and availability of IT services while boosting IT staff productivity.

Server virtualisation can help increase IT flexibility and reduce equipment and labour costs by consolidating applications and workloads onto fewer physical servers. Rather than using five separate physical servers for five distinct applications, enterprises can employ virtualisation software to run all five applications on the same physical server.

Server virtualisation offers several important advantages, but to realise the full benefits of server virtualisation, data centre managers must overcome significant storage challenges. In many data centres, those challenges arise because storage is directly attached to servers and cannot be shared beyond the physical server. Storage area networks (SANs) enable servers to share centralised resources but virtualising storage on a SAN is only the first step.
Traditional SAN offerings can experience some of the same stumbling blocks as direct attached storage in a virtualised environment. In fact, some of the shortcomings of direct attach storage and traditional SANs are actually exacerbated by server virtualisation. When virtualised server environments are coupled with traditional storage, it is more difficult for administrators to tailor storage requirements for each application.

An application might benefit from a particular server interface, drive technology or speed, RAID configuration, or snapshot schedule. But in a virtualised server environment with direct attached storage, all of the applications running on the physical server are forced to use the same storage, with the same storage characteristics. Traditional SANs do not provide a solution. Instead they offer only a limited number of volumes which are not enough to accommodate each of the large number of applications that can run on a virtualised server.

To take full advantage of server virtualisation, IT departments need a holistic storage solution that allows fully shared resources, easy and automated storage classification and migration, and complete data protection. It is only through virtualising both storage and servers (see diagram) that data centres can realise the full benefits of virtualisation and the promise of a virtual data centre.