Using RLUs to Determine In-Feed Capacities

In-feed capacities are the grand totals of the power, cooling, physical space, weight, and bandwidth you will need to support a given number of racks. Let's say you plan to build a data center with 40 Sun Fire 6800 servers (RLU-C). Each Sun Fire 6800 server will have four Sun StorEdge racks (RLU Superset-A) connected to it. That's 40 RLU-Cs and 160 RLU Superset-As.

The following table shows the total floor load support and in-feed requirements for these RLUs.

Table 4-3. Total In-Feeds for Racks

Specifications	40 RLU-C Racks	160 RLU Superset-A Racks	Totals
Weight	40,000 lbs (18,144 kg)	155,200 lbs (70,398 kg)	195,200 lbs (88,542 kg)
Power	160 30Amp 208V L6-30R outlets RM=2 339,506 W x RM = 679,012 W	320 30Amp 208V L6-30R outlets RM=2 657,778 W x RM = 1,315,556 W	480 30Amp 208V L6-30R outlets 1,994,568 W
Cooling	1,161,110	2,249,600	3,410,710
Physical space	24 in. x 53 in. = 360	24 in. x 48 in. = 1280	1,640 sq ft
Bandwidth Cat5: Fibre:	160 320	1,280	160 1,600

Only 40 to 60 percent of the floor space in a data center should be used to house machines, as the rest of the space is needed for aisles , row breaks, ramps, etc. Open space is also needed to allow cold air from the floor plenum to come up through perforated tiles to the racks, and for exhaust air to move freely out of the rack and into the HVAC return plenum.

So, multiply the total square footage by 2.0 to get the total square footage needed for the room.

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Now we can size our data center, right?

But wait, back the truck up! The architect just informed the electrical engineer that the VP of Human Resources has demanded a larger office and this will only allow us enough circuit breaker panel space for a 450 30A 208V circuit. Now what? We know we need 480 to support all of this equipment. We begged, pleaded, and explained to this VP that we need that space for the panels. No luck. Now it's a matter of reducing the equipment count until the total number of power outlets is reduced from 480 to 450.

Previously, we said that each Sun Fire 6800 server (RLU-C) would have four Sun StorEdge racks (RLU Superset-A) connected to it. The ratio for RLU-C to RLU Superset-A is 4 to 1. So if we remove three RLU-Cs, we remove 3 x 4 thirty Amp 208V or twelve 30Amp 208V outlets. Then we remove twelve RLU Superset-As, 12 x 2 thirty Amp 208V or twenty four 30Amp 208V outlets. This is a reduction of thirty six 30Amp 208V outlets. Now our new breaker panel requirements total 444 30Amp 208V outlets. We can get enough breaker panel space to run these devices.

Remember that the cooling, space, weight, and bandwidth requirements are reduced as well.

Not only do RLUs enable you to know what services (power, cooling, etc.) you need and where, they allow you to calculate how much you need. They also allow you to reverse engineer the number of racks you can support from any given in-feed limit you might have.