Enterprise Data Center Design and Methodology
| An RLU is a way to categorize the set of criteria for a rack of equipment that must be met for it to function. As previously described, these are power, cooling, physical space, weight, bandwidth, and functional capacity. The RLU tells you exactly what criteria needs to be meet for a rack of equipment to run. It doesn't matter what the empty space (places where machines do not live, aisles , pathways between aisles, door entries, etc.) has as criteria (it could be 90 degrees by the ramp). It also indicates where the physical attributes such as power outlets, cooling air, fibre connection terminations, etc., need to be located. They need to be located wherever the RLU will be located in the data center. To determine the bandwidth requirements for any RLU, you need to look at how the racks will be connected. The following table shows the RLUs created for three Sun products, Sun StorEdge T3 array for the Enterprise, Sun StorEdge A5200 array, and the Sun Fire 6800 server. Table 4-1. Sample RLUs
An individual Sun StorEdge A5200 array has up to four fibre connections. You can fit six Sun StorEdge A5200 arrays in a rack. If your environment only requires you to use two of these four connections (as shown in the table), then 2x6 will give you the correct count. However, if you use all four, the number will be 24. In the case of the Sun Fire 6800 server (RLU-C), the four Cat5 copper connections are necessary for these servers to be connected to two 100BaseT production networks, one administrative network, and one connection to the system processor. Now you have three RLU definitions: RLU-A, RLU-B, and RLU-C. If you have 30 different racks (all having differing specifications), you would have 30 separate RLUs. This is good, and each type of rack (having different specifications) should have its own RLU designation.
Note In this example, the definition names are alphabetical, but that only gives 26 possibilities (52 if using both upper and lower case). You can design your own alphanumeric designations. Whatever you choose, keep the designations short.
Notice that the definitions for RLU-A and RLU-B are similar. Power outlets are the same and watt usage is near identical. Cooling is a difference of only 1020 BTUs per hour . Physical space is the same. Weight difference is less then 100 kg. The biggest differences are bandwidth (and that is four fibre connections), and functional capacity at 0.5 terabyte. Therefore, by taking the worst case for each of the criteria you can create a superset RLU definition that will meet the requirements of RLU-A and RLU-B. (Keep in mind that a superset definition can combine as many racks as is practical.) For now, let us call this example RLU Superset-A. Table 4-2. Combining Two RLUs Into a Superset RLU
Note Using the "superset" name indicates that an RLU type is made up of the specifications of two or more racks. It is also a good idea to keep a list of the separate RLUs in each superset.
Assume a decision is made to install 60 RLU-A racks and 20 RLU-B racks in your data center. By building 80 RLU Superset-A locations in the data center you can support the 60/20 mix or any mix of 80 RLU-A and RLU-B racks in the data center. That gives you flexibility and leeway if you need to make adjustments. You now know exactly what you need (power, cooling, etc.) and where you need it for each rack going into the center. Using superset RLUs gives you flexibility in the design if you need to modify the number of racks later, with no need to retrofit. There is another benefit: Often most data centers are not at full capacity when they are built. By having pre-defined and pre-built RLU locations of given types, you can more easily track the RLU locations that are not in use. As you need to bring new racks online you know exactly how many you can install and where. |