Definition

A blade server is a mini version of a full-sized server that contains all of the computing resources of a full server but not all of the power and cabling.  Those functions are handed off to a blade enclosure, which allows for denser configurations than traditional server architectures and thus  provides greater computer power per square foot in the datacenter.

Business Applications

Blades can perform all of the functions of a standard server, and can therefore serve the entire range of business applications, from CRM and Business Intelligence to security, web hosting and application development.

Being small and compact, they are ideal for clustered server architectures. They are usually hot-swappable, allowing for easy scalability.

Blades can also be devoted to specialized purposes, such as switching, routing and storage. Indeed, it is common practice to devote one blade in the enclosure to a specific function so the others can focus on data and application processing.

Deployment Concerns

The chief concern with blades is power consumption.  While individual blades draw less power than standard servers, the fact that  you can pack three times as many blades onto the same floor space increases the  power draw for both processing and heat dissipation. The blade itself does not include a fan, so a fully loaded enclosure has to work extremely hard to keep the devices from overheating.

Newer blade enclosures feature more power fans and advanced power and cooling management technology to alleviate the problem, although it is still risky to load many enclosures past the halfway point. Some enclosures are starting to feature water-cooled designs.

Most blade servers are built on an open platform, theoretically allowing them to be mixed and matched in multi-vendor environments. In practice, though, this is more difficult than it sounds, with many users opting for single-vendor deployments for improved management and connectibility.

Technical details

A blade enclosure can hold up to 128 blades, compared to a standard rack of 42 servers. A typical blade will contain processors, a small amount of memory (usually an ATA or iSCSI drive), an integrated network controller and possibly an HBA or some other I/O port device.

More information on blade servers can be found at blade.org.