Data Centre Design - The basic considerations

13/06/2009 by David Slade.

Introduction

In order to design a suitable Data Centre for an organisation it is vital to consider a multitude of interconnected factors. In the fast moving world of IT, where the physical sizes of types of technology assets can change regularly, it is a challenging task to design a Data Centre that will cater for the needs of an organisation for the next ten years or more. This document will discuss some of the factors to be considered when developing the design of a Data Centre, and will provide advice on how to maximise the opportunities for future proofing the facility.

Location
Historically, most companies have based their Data Centre facilities within the same buildings as their staff. If this is the proposed strategy for your new facility, then you need to consider whether the Data Centre should be located on a basement floor or on an office floor. Typically, basement rents are approximately one quarter of office floor rents, and your stakeholders will probably prefer that you do not take up valuable office floor space with technology equipment that does not necessarily justify a prime location on the floor. Another factor to consider is support. If your
support staff require access to the facility on a regular basis then you need to determine whether it is acceptable for them to be continually going from the office floor to the basement.

Size
This is probably the most challenging factor of Data Centre design. In addition to rental costs, it is expensive to provide power and cooling facilities to large areas so you will be under pressure to make sure that the Data Centre is not excessively large for the requirements of the organisation. However, it can be equally expensive and time-consuming to extend a Data Centre that is initially designed too small. A reasonable method for calculating the size of the room is to plan for day one and then to add an additional 30% space for expansion. You also need to factor in whether mechanical and electrical plant will be located within the Data Centre and if so, to ensure that these devices are coordinated with the overall design of the room

Power
The design of the power solution will depend on the business need for the Data Centre to ‘stay up’. Where the failure of a Data Centre has direct financial implications for a company, then a business case needs to be established to understand the costs of a failure versus the expense of installing a highly resilient power solution. Similarly, if a temporary Data Centre failure does not directly affect the revenue generation of the organisation, then it could be seen as a waste of money to specify a highly resilient solution.
There are a number of resiliency factors to consider:

• Cabinet Power. Ideally, power strips within a cabinet should be fed from two separate Power Distribution Units (PDUs). This is relatively easy to implement at design stage but can be expensive to change later. Breaker sizes also need to be considered carefully, and will be defined by the equipment that you are planning to install on day one as well as the likely requirements for ‘future’ equipment.

• An Uninterrupted Power Supply (UPS) will allow devices to stay up while mains power is restored, or at least will allow equipment to be shut down safely. You might specify a central UPS that supports all Data Centre active equipment, or alternatively you might install separate UPS devices for each individual system. The important factor to consider is how long the IT team needs to safely power down systems in the instance of a mains power failure. The UPS design will be based on this important time period.

• A Generator can keep equipment running in the case of an extended failure of mains power. Generators can take up a significant amount of space as there is a requirement for the storage of fuel to run the generator. However, they are vital to organisations who cannot afford a power outage to affect their IT  operation.

Air Conditioning
As with power, the required level of resiliency will be determined by the costs to the business of Data Centre failure. An important consideration is that air conditioning units require chilled water to cool the environment, and where possible you want to ensure that water does not get inside your Data Centre. Consultants are now recommending the construction of a service corridor outside the Data Centre. This corridor contains the air conditioning units, which can blow cold air in to the room, but can also be serviced outside the room. The wall between the service corridor and the Data Centre is water sealed; therefore if an air conditioning unit should fail the water will not be able to penetrate the Data Centre.

Where it is necessary to install air conditioning units within the Data Centre, thought should be given to leak detection and also to the ongoing servicing of the units. Thought also needs to be given to UPS support for the air conditioning equipment: there is little value in IT equipment remaining up and running if it will overheat and fail due to a lack of available cooling.

Raised Floor
The height of the raised floor will be determined by a number of factors:

• Distance between the slab and the soffit. This distance might limit the amount of available space for the raised floor void.

• Height of the raised floor across the rest of the office space. Normally, the office floor will have a raised height of 200mm whereas the Data Centre raised floor height will be anywhere from 300mm to 750mm. In order the bridge the gap between these heights, steps and\or a ramp will need to be installed and space restrictions within the room might prove prohibitive.

• Depth of structured cabling. The air conditioning units generally tend to push cold air in to the floor void. For this system to work effectively there needs to be sufficient space for the air to circulate. Therefore, a large volume of structured cabling will require a higher raised floor to allow the cold air to circulate above it.

When installing a raised floor, thought also needs to be given to the size of floor tile that is specified. The majority of floor tiles are 600mm square, whereas the cabinets are 800mm square. When designing the cabinet layout, care should be taken to ensure that no tiles are ‘trapped’ and that the tile cut-outs are in sensible positions.

Suspended Ceiling
Consultants are now recommending that suspended ceilings are not installed in Data Centres. The recommended solution is for suspended light fittings to be hung from the soffit, and also for power to be presented at high level within containment also hung from the soffit. There are a number of advantages to this solution:

• Cost savings are achieved by removing the suspended ceiling from the construction budget.

• There is a greater fire risk when power and data cabling are located in close proximity. By locating data cabling in the floor void and power at high level, the risk of fire is significantly reduced.

• It is easier to control maintenance works within the Data Centre. The electricians will not need to get in to floor void, and the data cabling engineers will not be working anywhere near power.

• It is easy to ensure that cabinets are fed by power from two separate PDUs.

When power is installed within the floor void, power strips are often cabled to the same PDU and this is not known until failure occurs. When power is visible at high level, it is easy to identify poorly configured cabinets.

Whilst power at high level is an ideal solution, thought needs to be given to the configuration of cabinets. Only recently manufactured cabinets will have holes in the top for power cables to pass through, therefore older cabinets might need to be modified if no holes exist.

Fire Suppression

Most office floors are protected from fire by sprinkler systems (this is a requirement of ‘Section 20’ buildings). Data Centres also require protection, and this will normally take the form of a ‘pre-action’ sprinkler system or a gas based fire suppression system.

The following items are worth considering in your design:

• If power is presented at high level, there is a minimal risk of fire within a Data Centre. In this case, a sprinkler system might be the most cost effective system as it is highly unlikely to be ever be set off.

• Most gas based fire suppression systems work on the principle of reducing the percentage of oxygen within an enclosed space in order to extinguish a fire. These solutions require that the room is fully sealed to ensure that the gas does not seep out of the room when it is released. When carrying out new installations which require running cables in to the room, engineers need to ensure that the room is sealed after any work. If this does not happen then the gas might fail to extinguish the fire.

• The gas required to protect the space needs to ideally be stored relatively close to the Data Centre. Where you are protecting a large area, the gas bottles can take up a large amount of space within your building.

• The main positive of the gas based system is that if one piece of equipment catches fire, then the fire will be extinguished with hopefully no damage being done to your other equipment. Sprinkler systems can not necessarily claim this advantage.

• Fire protection can also be enhanced by the installation of a fire detection ‘sniffer’ aspirating system (VESDA) which samples the air and gives early warning of any hot spots within the room.
• Alternatively there are also water misting systems and N2 Oxy reduction systems, that have sometimes been installed.

Security
The criticality of most Data Centre facilities means that security is a vital element of the design process.

Items that need to be considered include:

• Is it acceptable for the Data Centre to be visible from outside the building? If no, then windows might need to be blacked out or an interior wall built between the glass façade of the building and the Data Centre.

• How many doors does a person need to get through before they can get access to the Data Centre? There is a balance to be found between locating a facility near to a goods lift to facilitate easy delivery of new hardware, and exposing the facility to risk of intrusion from external parties.

• It is good practice to ensure that security cameras monitor all entrances to the Data Centre.

• A permit to work system should be established for all Data Centres. Access to maintenance staff should only be allowed when the proper supervision is in place.

Operating Model
When designing the Data Centre, it is important to think through the operating model of the facility. If cabinets or servers need to be brought in to the Data Centre on a regular basis, you need to ensure that the facility is easily accessible from the goods lift, and also that the Data Centre doors are sufficiently high and wide to allow
cabinets to be taken in and out.

Mechanical consultants are also now recommending a hot aisle\cold aisle principle for cooling Data Centres. This requires that rows of cabinets face each other. This design will work effectively in a ‘lights out’ Data Centre but if you run a facility where cabinets are constantly being worked on, then it would be difficult for support staff to work on two cabinets that face each other. Therefore, the mechanical and electrical services designs need to reflect the operating model of the facility.

Off-Site Hosting Facilities
Companies are now able to benefit from remote Data Centre hosting facilities offered by third party vendors. These sites are designed to be highly resilient and to cater specifically for only the IT requirements of an organisation. One major advantage is that the IT strategy of an organisation can become relatively independent of the Facilities strategy.

For example if an organisation decided to relocate to a new HQ building, the majority of equipment can remain in the remote Data Centre, thus significantly reducing the cost and risk of the project.

The majority of remote Data Centres are also able to offer scaleable facilities. For example, on day one you might rent 12 data cabinets, with the option of increasing this whenever you need extra space. You can also build in to the contract an option to reduce space should the equipment you install become smaller in the future.
Again, this can significantly reduce financial risk for the IT Director.

Whilst these off-site facilities might initially seem expensive, when compared with the true cost of building and managing your own Data Centre, they can seem competitive.

The main negative of a remote Data Centre is that control is ceded to the third party that runs the facility. Whilst the majority of providers run highly professional facilities, they are unlikely to understand the urgency of fault diagnosis and resolution that your own internal staff would take for granted.

Summary
The sections above highlight a number of key areas that need to be considered when designing a Data Centre. As a facility of this kind is normally designed for a minimum ten-year period, it is unlikely that you can design the perfect environment. The best you can hope to do is to consider all of the design parameters outlined above and fit them to the technology requirements of your organisation.

Posted in Air Conditioning, Raised Floors, leak detection, Oxy reduction system, section 20 building, Facilities strategy, Suspended Ceilings, Fire Suppression, Uninterrupted Power Supply (UPS), Power Distribution Units (PDUs), Generator, resiliency, Section 20 buildings, Data Centre Design | 1 Comment »