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As customers look to grow their data centers or replace aging infrastructures, many are turning to blades to save space, increase density and decrease power consumption, while lowering total cost and improving infrastructure flexibility. Blade.org
Enterprises moving to blade servers can experience as much as an 85% reduction in cabling for blade installations over conventional 1U or tower servers... SearchDataCenter.com

Blade Servers


Definition
: blade servers are part of a computer configuration where power, cooling, storage and connectivity are largely provided by an outer housing or chassis. The chassis contains and services a number of specialised, stripped down motherboard units - the blade servers - each one a complete computer or service device containing only vital processing and storage elements.

Blade server technology was initially developed in the early millennium through a partnership between IBM and Intel. Later, a number of major companies, led by IBM, formed an “industry community” in February 2006, with a website base at blade.org. The mission of the community is to “accelerate the growth and adoption of [blade] technologies in the market.”
 

 

blade server
 


As part of the community development, similar to their action with PC specifications in the 1980s, IBM made the specifications for blade servers open allowing any manufacturer to develop and build blade server compatible products and solutions.

A number of computer manufacturers has consequently joined IBM and Intel in blade server manufacture. Some of the major players in the field include HP, Sun Microsystems, Dell and Hitachi.

The different blade manufacturers vary in specific configurations for their blade servers and chassis, but the basic principle remains: to strip extraneous components from the blades so the blades’ components can focus on essential processing and services.

Computing blade servers are unique computers, often dedicated to a single application, and the facilities they lack are provided either within the chassis, or, particularly with storage, over a network. However, not all blades are computing blades, but may instead provide connectivity, storage, system management or other services for the system or chassis’ blades’ benefit, or even the wider network.

Advantages of Blade Servers

The chassis and included blade servers may require a substantial initial investment in hardware and implementation for a business, even when compared to traditional rack-servers. However, blade servers bring advantages in space, power consumption, cable reduction, reliability, and economy of scale that may offer considerable longer term benefits.

The blade server model promotes thin-client computing, where in an enterprise environment workers can log on to their computer from remote terminals. At their office space, the worker has access to standard input and output functionality through keyboard, mouse and monitor. However, their PC is a blade (often termed a “PC blade”) held in a chassis, stored in a central, secure location, with centralised management and maintenance. In a wireless setting, they can work on their PC from anywhere in range. If the workplace’s network is accessible over the Internet, perhaps through a VPN (Virtual Private Network), then the worker can access their PC from anywhere they have access to a client computer and the web.

Of course a number of these advantages are offered by rackmount servers, but the distinct advantages of blade servers lie in redundancy, hot swapping, and reductions in cabling, power and size requirements. The net result is that cost reduction for a blade server versus a traditional rackmount server is claimed to be as much as 25%.

Blade Server Chassis

The chassis forms the housing for the blade servers, providing the necessary services for the blades. Chassis vary in the number of blades they accept, usually from 6 to 16, though this may be A typical blade server chassis halved with dual CPU blades of size 2U (1U=one rack unit, which is 44.45mm or 1.75”). However, much bigger blade compositions are possible in specialist large-scale requirements.

The services they provide include power, cooling and interfaces, enabling and augmenting the power of the blades themselves. Their design features will focus on connectivity, flexible configuration of blades, strong build for protection and cooling, and elimination of cabling requirements.

A blade chassis could theoretically support any blade, but in practice there are issues with manufacturer technologies. Chassis manufacturers may, at worst, support only their own blades, and though there are many open blade chassis architectures these invariably have limits on the blade server models they accept.

Hot Swapping

One of the important facilities available in blade server chassis is hot swapping. Hot swapping is the ability to add, remove and replace units at need without having to power-off the chassis. Hot swapping can apply to PSUs, network, management and storage units, and the blade servers themselves.

Hot swapping, coupled with redundancy, can give significant reliability benefits. For instance, with two PSUs, if one goes down the other can take over and maintain the system without interruption until the first is replaced. It also aids maintenance, because if a blade develops a problem it can be removed and repaired or replaced without disruption of the other blades in the system.

Power

Since the blade is stripped down of many key features, it relies on the chassis to provide vital services.  Power is the first of these, and in all chassis power switching balances power load and requirements across the component blades’ demands. The technology ensures that power isn’t wasted running underused blades, but in times of high demand there is sufficient power available.

Employing power supply unit redundancy is necessary for critical servers. The chassis’s internal management technology then monitors for malfunctioning units, and alerts network management staff. Hot switchable PSU’s enable the faulty components to be replaced without interrupting chassis function.

Cooling

A full chassis may generate considerable heat from the activity of component blades, so high demand blade servers require effective cooling from their chassis to operate efficiently.

The chassis’ internal management systems monitor heat within the system, and may shut down the entire system if the temperature rises above a certain point. It’s critical, then, to follow the directions of the blade server chassis’ manufacturer when managing the server’s cooling.  This might include air space around the chassis, the use of plugs for empty bays, and environmental demands for air temperature and humidity.

Connectivity

Blade servers always have some limited connectivity, if only Ethernet ports to connect to the chassis. The main external connectivity is by design provided via the chassis.

At the heart of the chassis’ connectivity will be an Ethernet and/or Fibre Channel switch, connecting each of the blade servers to the LAN (Local Area Network). There may be more than one switch unit in a chassis, which can either be used to provide a redundant connection to a single network, or connection to more than one network.

Other connectivity is also provided by the chassis, but this is typically limited to USB and VGA for monitor connection, with possibly PS2 connections for I/O with mouse and keyboard. It’s also likely that a chassis will contain an optical drive, although at need all of these functions and more can be added to the chassis through the use of specific blades in the system.

Storage

There may be some limited storage on a blade server, and there may be additional storage provided by a chassis.

However, with the use of a SAN (Storage Area Network) the chassis and blades can be completely free of storage, removing the inherent heat, noise, and reliability problems from the system completely. Everything from booting to data storage can be done over the SAN, enabling the blade servers to be focussed entirely on processing.

Blade Servers

Each blade server is a complete computer, albeit stripped of some functionality. A typical computing blade will contain one or two CPUs with supporting chipset on a specialised motherboard, RAM, and little else.

Despite the advantages of storage outside the blade chassis, many blades have the capacity to take one or two hard drives, usually SATA. Other functionality may beIBM HS20 blade server present, such as onboard graphics and VGA output, and USB connectivity, but the more technology that is held on the blade the less advantage is being taken of the benefits blade server architecture offers.

Although most blades provide computing services, there are other common functions that a blade can usefully provide. For instance, some blades are specifically designed to provide storage, offering a large number of hard drives. Others provide connectivity options and system management facilities. The configuration of blades and their functions can be balanced at the time of purchase and modified in ongoing use to meet particular business demands.

Blade servers typically have a front panel containing a number of informational LEDs, relating to power and system activity. There may additionally be indicators of system failure, which may be general or specific to blade components. These optional features will invariably come at a cost premium.