This content is part of the Essential Guide: Server form factors: A guide to rackmount, blade servers and more

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Things to know about blade server technology before you buy

If you're interested in blade server technology as an alternative to towers and racks, sharpen your knowledge with these facts.

Every data center starts with just a few servers. Not long ago, it was common to install tower servers in the data center, but today most tower models have been replaced with 1U rack servers or blade servers.

A blade server is a very small server designed to be as efficient as possible in the space it uses as well as with its energy consumption. Should you consider replacing all of your servers with blades? In this article, you'll find answers to the five most commonly asked questions about blade server technology.

What is a blade?

A blade server is a stripped-down computer optimized to consume a minimal amount of power and use the available space in a data center as efficiently as possible. Depending on the server vendor's design, server density with blades can be six times higher than that of regular servers.

Because efficiency is an important design goal for blades, only the core server components are on the blade itself. Everything that can be shared between servers is in the blade chassis. A blade cannot be used without the blade chassis, which provides vital functions like power, cooling, etc. If you're investing in a blade chassis, it follows that you don't buy just one blade server: You would buy a chassis to install multiple blades.

Storage usually isn't available on the blade; it's typically provided by a storage area network (SAN). The blade chassis is connected to the SAN and the blades themselves boot from the SAN. As blades normally don't have optical disk drives either, they typically are installed by using installation servers. Putting all this together, using blades makes the data center more efficient, but blades don't make the process of installation and maintenance any easier.

Are blade servers cheaper?

It depends. If you just need a few servers, then it's usually cheaper to buy 1U rack servers or even a cheap tower server -- prices start at about $300 for a minimal configuration.

You can't just buy one blade server, since blade server chassis are built for multiple blade servers.  Because it is so compact, the blade itself is more expensive -- prices start at about $ 1,500 -- and in addition to that you'll need a blade chassis as well. And, adding to the price, you'll need a storage solution and fast connectors. A complete blade server configuration will cost you much more than buying a couple of 1U servers.

So price is not a reason to buy blades. When buying blades, you're really buying power efficiency, because energy consumption per blade normally is much lower than power consumption per rack server, and they generate less heat than racks too, which helps save on cooling costs.

Let's make a rough calculation. If you've got a 1U server that consumes 400 W hourly and uses 9.6 kW daily, at a price of 20 cents per kW that is about $2 per day for power consumption -- $730 yearly. Over the average five-year lifetime of a server, power consumption would total $3,650, excluding the costs associated with cooling the 1U server. If eight blades in a blade chassis use 800 W hourly, or 100 W per blade, that means the yearly electrical cost is 25% less than a regular server. So buying a blade may be more expensive up front, but it can be cheaper to operate because of the reduced power consumption.

In addition to the reduction in power cost, consider the costs of the rack space you need in the data center for your blade. If you rent racks, you probably pay hundreds of dollars monthly for rental. If using blades to consolidate means eliminating a couple of racks, you may end up with a significant cost reduction by buying blades. Make those calculations before buying!

How do you boot from a blade that doesn't have a hard disk?

Diskless blades boot from the SAN. While setting up the blade, you just tell it which logical unit number  to use. In a Fibre Channel SAN, this is easy; you almost don't see the difference between a local disk and the disk on a SAN. The only issue is you might need to tell the operating system (OS) that it is booting from a SAN. Some OSes need additional drivers to boot from a SAN, so make sure that it is supported by the operating system you want to use. This shouldn't be an issue for modern server operating systems.

Does it make sense to use blade server technology in small to medium-sized companies?

It all depends on the number of servers you want to use. If you just need four servers, don't go for a blade solution. With eight or more servers, a blade solution may be worth considering. It's true: You need a shared storage solution as well, but shared storage solutions are already used in many companies. So even for small and medium-sized companies, a blade-based server solution may be within reach.

What are the alternatives?

There's a trending technology that has similarities to blade servers: the microserver. Microservers are low-capacity servers that are installed in a chassis as well. A typical configuration allows you to connect 12 microservers in one chassis. If you need powerful servers, look at a blade solution. If you need physically isolated servers to run tasks that don't ask much of the server hardware, then installing microservers might be the better solution.

ABOUT THE AUTHOR: Sander van Vugt is an independent trainer and consultant based in the Netherlands. He is an expert in Linux high availability, virtualization and performance, and has completed several projects that implement all three. He is also the writer of various Linux-related books, such as Beginning the Linux Command Line, Beginning Ubuntu Server Administration and Pro Ubuntu Server Administration.

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