In the world of data-center computing, there's a lot of contention over whether deploying rackable servers is better than deploying blade servers to host consolidated or virtualized applications.

Because IBM has been a top performer in recent server tests, for this hands-on exploration of blades vs. rackable servers, we tested IBM's state of the art in both categories -- the HS21 and HS21 XM blades and the x3550 and x3650 rackables -- and focused on performance, power consumption and manageability.

Because blade offerings have at least some things in common, we believe these test results are applicable generally to blades from other vendors -- Dell and HP, for example -- though there may be vendor-specific considerations in assessing products from others.

We found that blade servers reduce but don't eliminate redundant hardware components requiring electrical power, a pivotal consideration in total cost of ownership (TCO). That said, while IBM's blade servers equaled the performance of its rackables, the blades were more power efficient and potentially much easier to service.

While rackables are less expensive than blades when buying only one or two servers, because you have to factor in the cost of the blade chassis, a fully configured blade chassis is the more economical hardware buy than purchasing the same number of rackable servers. On the other hand, adopting a blade configuration demands a vendor lock-in that rackables don't, because they can be added one at a time as needed. Also, blades fall short for applications that require large amounts of on-board storage.