Going virtual raises storage-management issues

What to think about when considering deploying storage virtualisation.

These concerns are especially true when it comes to thin provisioning, a component of virtualization technology that lets an IT administrator present an application with more storage capacity than is physically allocated to it. This eliminates the problem of storage over-provisioning, in which storage capacity is pre-allocated to applications but never used.

With thin provisioning, more than 100 percent of storage capacity can be allocated to applications, but capacity remains available because it won't be consumed all at once.

You can play it safe by allocating small volumes that never exceed the physical storage, or allocate as much as you want to each application, then monitor your systems closely, says Themis Tokkaris, systems engineer at Truly Nolen Pest Control in Tucson, Ariz. It's best if you can find a happy balance between those two extremes.

"You have to monitor your pool so you don't run out of space, because that would really crash everything," Tokkaris says.

How server virtualization fits in

A common question is whether it makes sense to virtualize storage if you're not also using server virtualization. The short answer is yes -- though it's true you won't get as much flexibility as IT shops that virtualize both servers and storage.

"If you virtualize both, then you have the maximum flexibility when deploying new applications," says Chris Saul, IBM's storage-virtualization marketing manager.

Nevertheless, there are benefits to just virtualizing storage.

Improved disaster recovery, availability and data migrations can all be gained without having virtual servers, says product marketing manager Augie Gonzalez of storage virtualization vendor DataCore Software. In addition, storage virtualization by itself can provide thin provisioning, as well as the simplified management structure that comes with pooling storage devices and managing them from a central console.

On the flip side, virtualizing servers without virtualizing storage is problematic. It doesn't make sense to have multiple virtual servers on a physical machine that aren't able to share data, says Enterprise Strategy Group (ESG) analyst Mark Peters.

"You can gain tremendous benefits from storage virtualization, even without server virtualization. It's harder the other way around," Peters says.

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