As you plan for server implementation, you'll need to decide what type of server is best for your situation. Two common form factors, or physical configurations, for servers are rack and blade. Your decision for implementation will be based on a variety of factors, including, but not limited to, cost, available space, size of organization and nature of application to be provided.
The distinction between rack and blade servers is misleading, as virtually all blade servers are technically constructed so they can be mounted in a server rack. With this being said, rack servers are computers that are designed to be stand-alone machines, running a specific number of applications and are separate, distinct servers. Blade servers consist of a chassis that houses small form-factor servers, which operate as individual computers.
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Rack servers are designed to be installed in computer or server racks. These enclosures range in size, from 23 inches wide by 36 inches deep by 36 inches high all the way to 24 inches wide by 36 inches deep by 84 inches high. Rack server height is measured in units called a "U." A U is approximately 1.75 inches in height.
A blade server is a chassis or shell that houses multiple physical servers or blades inside of it. The entire system is oftentimes rack mounted. Blade servers range in size, but they typically are between 4 and 8 Us in size. The chassis is rectangular, just like rack servers, but the individual servers housed in it are often installed so that they are perpendicular to the blade enclosure. Within an 8U amount of space, a blade server can physically house 16 to 32 or more blades.
Rack servers range in price, depending on the amount and quality of the hardware components in the server itself. Entry-level rack servers start at $700 and can scale all the way to $6,000 per server. Again, this is for a single, stand-alone server.
Blade servers range in price as well, but with the understanding that they are more expensive the more blades you add inside of the chassis. Entry-level blade enclosures start around $2,000 and can cost as much as $15,000 or more. This is for just the chassis and not for each individual blade. A blade can be as cheap as $500 but will range all the way to $2,000 a piece.
Choose your server type by what your needs are. If your organization currently needs or will need a large number of servers, then consider blade server technology. In addition to being more space efficient, they tend to be more energy efficient than having an equivalent number of stand-alone rack servers individually powered. If you are looking at your options for a smaller business, consider a rack server. From a one-to-one comparison, the blade server chassis and single blade server is significantly more expensive than a single rack server. A blade server doesn't become cost effective until you have a significant number of blade servers housed in the enclosure. Also, if the blade server chassis stops working, this will affect all the blades housed in the enclosure.
What is becoming popular is using both rack and blade servers to host multiple virtual servers. Virtualization allows a single server, whether rack or individual blade server within a blade chassis, to run multiple virtual or software-enabled servers. This virtualization software emulates all the physical components of a server, such as hard drives, processors, RAM, etc. This technology can be used on both rack and blade servers.