Reference
Data centre glossary
Plain definitions of the 38 terms that come up most in data centre smart hands work, from cross-connects and meet-me rooms to DWDM and optical budgets. Each one is written to stand on its own, and links to the service that does the work where that applies.
A to Z
Terms and definitions
A
- A and B feedsDual feed
- A and B feeds are two independent power supplies into a cabinet, each from a separate upstream path, so that losing one leaves equipment running on the other. The arrangement only works if the load is balanced such that either feed alone can carry it, which is why measured draw matters more than nameplate ratings.Power and connectivity
- As-built documentation
- As-built documentation records what was actually installed, as opposed to what the design said would be installed. It typically covers rack elevations, cable runs with both ends labelled, serial numbers and circuit references. It is the difference between an estate you can change safely and one where every job starts with an investigation.Audits and documentation
C
- CabinetRack
- A cabinet is the enclosed frame that holds data centre equipment, usually 42 to 52 rack units tall and fitted with lockable doors. Cabinets are the unit in which colocation space is normally sold and the boundary within which most smart hands work happens.Rack and stack
- Cage
- A cage is a physically separated area of a data hall enclosed by mesh walls, containing one customer's cabinets. Cages are used where a customer needs more space than a few cabinets, or where compliance requires their equipment to be physically segregated from other tenants.
- Carrier hotel
- A carrier hotel is a building where a large number of network operators terminate and interconnect their networks. They tend to be older, centrally located buildings that accumulated carrier presence over decades, which makes them expensive but hard to replace. 60 Hudson Street in New York and the London Docklands campuses are typical examples.
- Cat6a
- Cat6a is a copper cabling standard supporting 10 Gigabit Ethernet over distances up to 100 metres. It is the usual choice for structured copper cabling in modern data centres, where earlier categories cannot sustain 10G across a full channel.Structured cabling
- Change window
- A change window is an agreed period during which work that could disrupt a service is permitted. Data centre work is frequently scheduled into overnight or weekend windows so that any interruption falls outside business hours. Work that overruns its window is normally rolled back rather than continued.Data centre migrations
- Coarse wavelength division multiplexingCWDM
- CWDM carries several channels over one fibre pair by spacing each on its own wavelength, 20nm apart, supporting up to 18 channels. The wide spacing allows uncooled lasers, which keeps costs down, but the channels fall outside the amplification window, so CWDM is generally limited to shorter metro links.Fibre design and DWDM
- Colocation
- Colocation is renting space, power and cooling in someone else's data centre for equipment you own and operate. The facility operator provides the building, power and physical security; everything inside the cabinet remains the customer's responsibility, which is where smart hands providers come in.
- Configuration management databaseCMDB
- A CMDB is the system of record for what infrastructure an organisation owns and how it is configured. Its usefulness depends entirely on how closely it matches physical reality, which is why a CMDB that has not been reconciled against the hall in years is often worse than no record at all.Audits and documentation
- ContainmentCable tray
- Containment is the tray, basket and ladder infrastructure that carries cables between cabinets and rows, usually overhead or under a raised floor. Well-planned containment keeps power and data separated, respects bend radius, and leaves capacity for cables that have not been installed yet.Structured cabling
- Crash cart
- A crash cart is a mobile trolley carrying a monitor, keyboard and mouse, used to work directly on a machine that cannot be reached over the network. Smart hands engineers use one when a device needs console access to be diagnosed or recovered.24/7 smart hands
- Cross-connect
- A cross-connect is a direct physical cable between two parties inside the same facility, typically running through the meet-me room. It is how a customer reaches a carrier, a cloud on-ramp or another tenant without traversing the public internet. Cross-connects are ordered from the facility operator and usually carry a recurring charge.Power and connectivity
D
- Dark fibre
- Dark fibre is optical fibre leased without any transmission equipment attached, leaving the customer to light it themselves. It gives complete control over capacity and protocol, and is the usual foundation for a DWDM or CWDM system between sites.Fibre design and DWDM
- Data centre infrastructure managementDCIM
- DCIM is software that tracks the physical layer of a data centre: rack space, power draw, cooling and connectivity. It answers questions like which cabinet has capacity and what would be affected if a circuit failed, provided the data feeding it is accurate.Audits and documentation
- Decommissioning
- Decommissioning is the controlled removal of equipment from service, covering shutdown, disconnection, removal, data handling and space handback. Done properly it also ends the billing for the space, power and cross-connects involved, which is the step most often forgotten.Data centre migrations
- Dense wavelength division multiplexingDWDM
- DWDM carries many independent channels over a single fibre pair by assigning each one its own closely spaced wavelength, typically 0.8nm apart or less. It supports 40, 80 or more channels and works with optical amplification, which makes it the standard approach for long-haul and high-capacity data centre interconnect.Fibre design and DWDM
E
- Elevation drawing
- An elevation drawing shows what occupies each rack unit in a cabinet, from top to bottom. It is the reference an engineer installs against, and the document that should be updated when anything changes, so that the next person starts from fact rather than from memory.Rack and stack
F
- Fusion splicing
- Fusion splicing joins two optical fibres by aligning the cores and fusing them with an electric arc, creating a permanent low-loss joint. It is used where a connector would add unacceptable loss or where cables must be joined mid-route, and each splice is normally verified with an OTDR trace.Fibre design and DWDM
H
- Hot aisle and cold aisle
- Hot aisle and cold aisle is a data hall layout where cabinets face each other in alternating rows so that intakes draw from one aisle and exhausts vent into another. Keeping the two air streams separate is what allows a facility to cool efficiently, and is why equipment should always be installed facing the intended direction.Rack and stack
I
- Insertion loss
- Insertion loss is the reduction in optical power caused by adding a component to a link, such as a connector, splice or multiplexer, measured in decibels. Every element in an optical path contributes some, and the total must sit within the link's optical budget for the connection to work reliably.Fibre design and DWDM
- Internet exchangeIX
- An internet exchange is shared infrastructure where networks interconnect and exchange traffic directly rather than paying a transit provider to carry it. Large exchanges such as DE-CIX in Frankfurt, AMS-IX in Amsterdam and LINX in London are a major reason customers place equipment in those cities.
M
- Meet-me roomMMR
- The meet-me room is the neutral space in a facility where carriers and customers physically interconnect. Cross-connects are patched here, which makes it the point at which responsibility passes between a customer, the facility operator and a carrier.Power and connectivity
- Multi-mode fibre
- Multi-mode fibre has a wider core that allows light to travel along several paths, which limits usable distance but permits cheaper optics. It is normally used for short runs inside a data hall, where distances are measured in tens or hundreds of metres.Structured cabling
O
- Optical budget
- The optical budget is the total loss an optical link can absorb and still work, calculated from the transmitter power and the receiver's sensitivity. A sound design measures the real loss of the route rather than estimating it, and leaves margin for ageing and for the extra splices a future cable repair will add.Fibre design and DWDM
- Optical time domain reflectometerOTDR
- An OTDR tests an optical fibre by sending a pulse of light and measuring what reflects back along its length. It reveals the true length of a route and the position of every splice, connector and fault, which is why it is used both to commission new links and to locate breaks in existing ones.Fibre design and DWDM
P
- Patch panel
- A patch panel is a fixed array of ports that terminates permanent cabling, so that day-to-day changes are made with short patch leads rather than by disturbing the installed infrastructure. Clear port mapping and labelling on a panel is what keeps later changes quick instead of risky.Structured cabling
- Peering
- Peering is an arrangement where two networks exchange traffic directly, usually without payment, rather than routing it through a transit provider. It reduces cost and often latency, and is a common reason for placing equipment where an internet exchange is present.
- Power distribution unitPDU
- A PDU distributes electrical power to equipment within a cabinet, in the manner of an industrial power strip built for rack mounting. Metered and switched models report draw per outlet and allow remote power cycling, which makes them valuable when nobody is on site.Power and connectivity
- Power usage effectivenessPUE
- PUE measures how much of a facility's total power reaches the computing equipment, expressed as total power divided by IT power. A PUE of 1.0 would mean no overhead at all, and modern efficient facilities typically report figures somewhere between 1.1 and 1.5.
R
- Rack unitU
- A rack unit is the standard vertical measure of rack-mountable equipment, equal to 44.45mm or 1.75 inches. Equipment is described by how many units it occupies, so a 2U server takes twice the height of a 1U one, and cabinets are sized by how many units they hold.Rack and stack
- Remote hands
- Remote hands is simple, prescriptive physical work carried out in a data centre on your instruction, such as power cycling a device, reseating a cable or reading a status light. The defining characteristic is that you supply the diagnosis and the instruction, and the person on site executes it.24/7 smart hands
- Return merchandise authorisationRMA
- An RMA is the vendor's authorisation to return a failed component for repair or replacement, and by extension the process around it. The physical work of removing the part, packaging it to the vendor's requirements and installing the replacement is normally handled by whoever has hands at the site.RMA and logistics
S
- Single-mode fibre
- Single-mode fibre has a narrow core that carries light along a single path, which allows far greater distances than multi-mode at the cost of more expensive optics. It is the choice for links between buildings and between cities, and the medium DWDM systems run over.Fibre design and DWDM
- Smart hands
- Smart hands is skilled technical work performed on site on your behalf, where the engineer contributes judgement rather than only presence. It covers installing and configuring hardware, tracing faults, terminating and testing fibre, and troubleshooting alongside your own engineers over the phone.24/7 smart hands
- Structured cabling
- Structured cabling is planned, documented copper and fibre infrastructure installed to a standard rather than run ad hoc as needs arise. Installing it properly costs more at the outset and repays that repeatedly, because every later change becomes a patch lead rather than an investigation.Structured cabling
T
- TransceiverOptic, SFP
- A transceiver is the pluggable module that converts between electrical signals inside a device and optical signals on a fibre. Form factors such as SFP, SFP+ and QSFP determine the speeds supported, and the transceiver must be matched to the fibre type and the distance of the link.Fibre design and DWDM
U
- Uptime SLA
- An uptime SLA is a contractual commitment to a percentage of availability over a period, with agreed remedies if it is missed. It should not be confused with a response SLA, which commits to how quickly someone attends rather than to the service staying up.24/7 smart hands
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