Just 30 years ago, a high-end computer easily filled an entire room. But such "big iron" systems are now the exception. Most modern data centers consist of racks of servers. Over time, systems have shrunk to the point at which a rack can easily hold a dozen servers, but the need for more power in less space continues.
Blade servers are the next advancement in the ever-shrinking hardware footprint. They look similar to PCs but are designed for mounting in a rack. A few years ago, a rack-mounted server commonly required two or three mounting bracket units—2U (3.5") or 3U (5.25")—of cabinet space. More recently, manufacturers have started introducing systems that require only 1U (1.75") of cabinet space. Suddenly a rack that was limited to holding nine or ten 2U servers can house twenty servers.
Reducing the server footprint eases systems management because it lets data centers expand their capabilities without increasing the size of their facilities. The latest improvement is known as the Web blade. Web blades fit into a blade server and provide a greater density of servers in less space and lessen maintenance costs by reducing the number of components that can fail. Because Web blades operate on the basis of scaling out, they're ideal for load balancing Web sites but aren't well suited for, say, clustering solutions. However, manufacturers are making the move to combine the scalability of Web blade-server architecture with fault-tolerant server architecture to maximize reliability and scalability.
Web Blades
Although the term Web blade is relatively new, some companies such as Cubix have been designing blade servers for years. Instead of mounting individual systems horizontally, as in a conventional server rack, you mount each Web blade vertically in a blade server. In essence, the blade server provides a common backplane for the Web blades to snap into. In addition to enabling increased density, reduced cabling, and shared power, a blade server uses one set of baseline components (e.g., CD-ROM or DVD drive, power supply, network cards) to support multiple Web blades. These shared resources help to reduce maintenance costs and power consumption.
The blade-server market is growing fast, and several new entries, including Dell's PowerEdge 1655MC, the IBM eServer BladeCenter, and Hewlett-Packard's (HP's) ProLiant BL20p G2, have emerged during the past year. However, not all players in this market are new. For example, Cubix has been working in the blade-server market for almost 10 years. The company's latest product, the BladeStation, squeezes up to seven Intel Xeon dual-processor Web blades into 6U (10.5") of rack space. The design supports four hot-pluggable SCSI drives on each Web blade. The design is supported by a scalable array of power supplies that reduce power requirements over a series of 1U servers and provide redundant power across the systems. A Web blade configuration costs about the same as a standard server setup; the BladeStation starts at less than $3000.
Although blade-server manufacturers often work on the leading edge of technology, some of their blade-server rack designs are compatible only with blade servers from the same manufacturers, leading to the perception in the IT industry that blade servers are proprietary. To overcome this perception, blade-server manufacturers are starting to ensure that their systems contain open architectures. For example, Cubix's XP4 blade server includes a standard PCI slot that lets you add a generic acceleration card or a product such as 14 South Networks' SlotServer, which can provide firewall capabilities at the server level.
Another 14 South Networks blade-specific product, the SlotShield PCI card, lets administrators offload firewall and other server security capabilities from a blade-server's processor. For example, in a Web hosting environment or in those instances where you want to assign one blade in a blade server to meet the needs of a particular customer, the SlotShield card lets the server become a standalone solution.
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