Racks and Enclosures

Racks are not dumb shelves you keep in your data center. They hold mission critical equipment and therefore require careful planning when you buy them

Friday, September 05, 2008

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Racks and enclosures form an important aspect of data center management. To add to the overall efficiency of your data center you need to maintain a congenial environment for servers, storage boxes, network switches, etc.

Thinking of racks and enclosures as just dumb shelves is a huge mistake no IT manager should make. However, buying racks and the right accessories for your data center is not an easy task. Lots of engineering goes behind maintaining and designing your datacenter. All IT equipment needs to be well connected to the data center's network. This is what calls for custom racks that best suit your needs. Your racks must have sufficient cooling fans and air distribution units to dissipate heat and be equipped with enough power distribution units to power all equipment inside. Proper cable management is equally important. You need to choose the right kind of enclosures as frequent assembling & disassembling can be a sheer nightmare for IT managers. Let's get into more detail of what you need to keep in mind before buying racks for your data centers.

Analyze your requirements
You need to consider several aspects before buying racks and enclosures. Racks and equipment that go into it should be standards compliant, so you should first get the dimensions of all your equipment. Racks are a long-term investments so you have to carry the capacity planning for your datacenter keeping in mind your future procurements plan. Besides, requirements for accessories keep increasing, so you should ensure that you are not short of space in your racks in near the future.

Pricing
Incidentally, every single accessory that you add to your rack will cost you. So, before you go and ask for a quote of racks, it's better to do your homework well, to avoid getting fooled by the vendor. You obviously don't want to end up with unwanted accessories imposed upon you. There are plenty of sites that will tell you about the kind of accessories available for racks.

Size and dimensions
The size of racks depends on how much equipment you plan to purchase and the floor space available in your data center. How the size of a rack is measured? The standard measurement of a rack is done in terms of rack units, where 1 rack unit (also known as 1U) is 1.75 inches tall. There are multi U racks available in the market, such as 42U, 45U, 48U etc. This means, in a single 42U rack, 42 servers or other electronic equipment of 1U height each can be stacked up. And of course, there are lots of equipment that are of 2U and 4U size.

A standard which is used to define different features of racks such as, rack unit, vertical and horizontal hole spacing, rack opening width etc. This has been defined by EIA (Electronics Industries Association). Unfortunately, this standard fails to define each and every detail of a rack. Therefore even when you buy a rack that follows these standards, chances of your server or other electronic equipment not fitting in still exist. For instance it doesn't define whether a rack should have two or four posts, how deep should it be, whether the rack holes are square or round (though square holes are most common these days), the distance between the two front posts etc. Another interesting fact is, the most commonly available 19 inch racks can't accommodate servers of the same width.

Rack types
Three types of racks are available today: 4 post, 2 post and wall mountable. The nomenclature behind them is simple. A 4 post rack has four upright angles to hold all the equipment and likewise, 2 posts have two such uprights. Further classification of a 4 post rack can be into an open frame or a closed frame rack. An open frame rack doesn't have any side panels, or front and rear doors. The one that does have these is a closed frame. Open frame racks are cheaper because of less use of metal. But one disadvantage of closed frame is restricted access to cabling due to an enclosed design.

The 2 post racks generally don't have any panels. They are cheaper, but look more cluttered. These can generally be used where space is at a premium. Most of these racks find use where either the requirement is only of two to three racks or in huge data centers where space utilization and cooling becomes a priority. Usually racks are made of aluminum extrusion which gives it strength and lighter weight with threaded holes on them. There are also transportable, wall mountable, and portable racks. All these are smaller and can be moved around easily.

Heating issues
What forms an important part of a rack is airflow. There are different technologies used for airflow inside a rack. You should check if the cooler air is able to reach the equipment inside the racks. There are also rack doors with perforation.

Racks of glass doors use alternative methods of cooling. The air is not let freely in and out of the data center, but pushed through the rack, from the raised floors.

There are also special air distribution units attached at the bottom of the rack, which would suck in air from the raised floor.

For cooling racks, enclosure blowers and fan systems are another solution. Here blowers and fans are installed inside the racks for efficient removal of heat.Using the surrounding cooler air, these blowers and fans get rid of the heat generated inside.

Optimally placing these equipment inside the rack is essential for maximum performance.

Cooling in high density racks
Unless you want your data center to turn into an electric furnace for your equipment, cooling remains an important issue to keep in mind. Many high density equipment are available these days for data center.

For example, Blade servers generate a lot of heat because they are all packed so closely together. For this you would require a special air removal unit or a roof fan tray in case you want proper exit for the hot air inside racks.

Like in nuclear reactors and power plants, special liquid cooling packages are also available for racks. These packages are intelligently built for optimum use of power supply, i.e. water flow and fan speed can be controlled according to the heat generated. One can also use chillers for effective cooling of racks. These come in variable sizes and mostly have removable panels for easy access for servicing.

Equipping racks with temperature and humidity sensors and controllers can also prove to be very efficient. These sensors can further be connected to your data center network, thus allowing you to monitor and control the temperature and humidity in a data center.

Cable management
While setting up a new rack, cabling should carefully be taken care of. As data center people have to move equipment around, in a data center to troubleshoot faults etc. the cabling generally becomes a complete mess. Hence, a rack which is designed to help manage cabling would be a good choice. The cabling in racks can come through the raised floor or from the ceilings. In any case, racks should have proper guides to ensure proper cable management.

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