This section of our two part series on tier 3 data center specifications deals with the power supply aspects.
As the most critical part of business, an organization needs to ensure 100% availability for its data center. This is why building a data center according to tier 3 data center specifications
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A data center built according to tier 3 data center specifications should satisfy two key requirements: redundancy and concurrent maintainability. It requires at least n+1 redundancy as well as concurrent maintainability for all power and cooling components and distribution systems. A component’s lack of availability due to failure (or maintenance) should not affect the infrastructure’s normal functioning.
These specifications have to be met only from the power, cooling and building infrastructure fronts till the server rack level. Tier 3 data center specifications do not specify requirements at the IT architecture levels. By leveraging the following steps, your data center’s power supply infrastructure can meet the tier 3 data center specifications.
Stage 1: Power supply from utility service provider
The Uptime Institute regards electricity from utility service providers as an unreliable source of power. Therefore, tier 3 data center specifications require that the data center should have diesel generators as a backup for the utility power supply.
An automatic transfer switch (ATS) automatically switches over to the backup generator if the utility power supply goes down. While many organizations have just a single ATS connecting a backup generator and power supply from the utility service provider, the tier 3 data center specifications mandate two ATSs connected in parallel to ensure redundancy and concurrent maintainability. The specifications however, don’t call for the two ATSs to be powered by different utility service providers.
Stage 2: Backup generators
Tier 3 data center specifications require the diesel generators to have a minimum of 12 hours of fuel supply as reserves. Redundancy can be achieved by having two tanks, each with 12 hours of fuel. In this case, concurrent maintainability can be ensured using two or more fuel pipes for the tanks. Fuel pipes can then be maintained without affecting flow of fuel to the generators.
Stage 3: Power distribution Panel
The power distribution panel distributes power to the IT load (such as servers and networks) via the UPS. It also provides power for non IT loads (air conditioning and other infrastructure systems).
Redundancy and concurrent availability can be achieved using separate power distribution panels for each ATS. This is because connecting two ATSs to a panel will necessitate bringing down both ATS units during panel maintenance or replacement. However, the tier 3 data center specifications require two or more power lines between each ATS and power distribution panel to ensure redundancy and concurrent maintainability. Similarly, each power distribution panel and UPS should also have two or more lines for the same purpose.
Stage 4: UPS
Power from the distribution panel is used by the UPS and supplied to the power distribution boxes for server racks as well as network infrastructure. For example, if a 20 KVA UPS is required for a data center, redundancy can be achieved by deploying two 20 KVA UPS or four 7 KVA UPS units. Redundancy can even be achieved with five 5 KVA UPS units.
The tier 3 data center specifications require that each UPS be connected to just a single distribution box for redundancy and concurrent maintainability. This ensures that only a single power distribution circuit goes down, in case of a UPS failure or maintenance.
Stage 5: Server racks
Each server rack must have two power distribution boxes in order to conform to tier 3 data center specifications. The servers in each rack should have dual power supply features so that they can connect to the power distribution boxes.
A static switch can be used for devices which lack dual power mode features. This switch takes in supply from both power distribution boxes and gives a single output. The static switch can transfer from a power distribution box to another in case of failures, within a few milliseconds.
About the author: Mahalingam Ramasamy is the managing director of 4T technology consulting, a company specializing in data center design, implementation and certification. He is an accredited tier designer (ATD) from The Uptime Institute, USA and the first one from India to get this certification.
(As told to Harshal Kallyanpur)
This was first published in March 2011