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CIT 668: System Architecture

Data Centers I

Topics

Data Center: A facility for housing a large amount of computer or communications equipment.

1. Racks

2. Power

3. PUE

4. Cooling

Google DC in The Dalles, OR

Located near 3.1GW hydroelectric power station using Columbia River dams for power

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Google Data Center in The Dalles, OR

Inside a Data Center

Inside a Container Data Center

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Data Center is composed of:

• A physically safe and secure space

• Racks that hold computer, network, and storage devices

• Electric power sufficient to operate the installed devices

• Cooling to keep the devices within their operating temperature ranges

• Network connectivity throughout the data center and to places beyond

Data Center Components

Data Center Tiers

See http://uptimeinstitute.org/ for more details about tiers.

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Racks

Racks: The Skeleton of the DC

• 19” rack standard – EIA-310D

– Other standard numbers.

• NEBS 21” racks – Telecom equipment.

• 2-post or 4-post

• Air circulation (fans)

• Cable management

• Doors or open

Rack Units

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Rack Sizes

http://www.gtweb.net/rackframe.html

Rack Purposes

Organize equipment – Increase density with vertical stacking.

Cooling – Internal airflow in rack cools servers.

– Data center airflow determined by arrangement of racks.

Wiring Organization – Cable guides keep cables within racks.

Rack Power Infrastructure

• Different power sockets can be on different circuits.

• Individual outlet control (power cycle.)

• Current monitoring and alarms.

• Network managed (web or SNMP.)

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Rack-Mount Servers

4U

1U

Blade Servers

Buying a Rack

Buy the right size

– Space for servers.

– power, patch panels, etc.

Be sure it fits your servers.

– Appropriate mounting rails.

– Shelves for non-rack servers.

Environment options

– Locking front and back doors

– Sufficient power and cooling.

– Power/environment monitors.

– Console if needed.

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Space

Aisles Wide enough to move equipment.

Separate hot and cold aisles.

Hot spots Result from poor air flow.

Servers can overheat when average room temperature is too low.

Work space A place for SAs to work on servers.

Desk space, tools, etc.

Capacity Room to grow.

Power

Data Center Power Distribution

http://www.42u.com/power/data-center-power.htm

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UPS (Uninterruptible Power Supply)

Provides emergency power when utility fails – Most use batteries to store power

Conditions power, removing voltage spikes

Standby UPS

• Power will be briefly interrupted during switch

• Computers may lockup/reboot during interruption

• No power conditioning

• Short battery life

• Very inexpensive

http://myuninterruptiblepowersupply.com/toplogy.htm

Online UPS

• AC -> DC -> AC conversion design • True uninterrupted power without switching • Extremely good power conditioning • Longer battery life • Higher price

http://myuninterruptiblepowersupply.com/toplogy.htm

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Power Distribution Unit (PDU)

Takes high voltage feed and divides into many 110/120 V circuits that feed servers.

– Similar to breaker panel in a house.

Estimating Per-Rack Power

The Power Problem

• 4-year power cost = server purchase price.

• Upgrades may have to wait for electricity.

• Power is a major data center cost

– $5.8 billion for server power in 2005.

– $3.5 billion for server cooling in 2005.

– $20.5 billion for purchasing hardware in 2005.

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Measuring Power Efficiency

PUE is ratio of total building power to IT power; efficiency of datacenter building infrastructure

SPUE is ratio of total server input to its useful power, where useful power is power consumed by CPU, DRAM, disk, motherboard, etc.

Excludes losses due to power supplies, fans, etc.

Computation efficiency depends on software and workload and measures useful work done per watt

Power Usage Efficiency (PUE)

Power Usage Effectiveness (PUE)

PUE = Data center power / Computer power

– PUE=2 indicates that for each watt of power used to power IT equipment, one watt used for HVAC, power distribution, etc.

– Decreases towards 1 as DC is more efficient.

PUE variation

– Industry average > 2

– Microsoft = 1.22

– Google = 1.19

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Data Center Energy Usage

Sources of Efficiency Losses

UPS

– 88-94% efficiency

– Less if lightly loaded

PDU voltage transformation

– .5% or less

Cables from PDU to racks

– 1-3% depending on distance and cable type

Computer Room Air Conditioning (CRAC)

– Delivery of cool air over long distances uses fan power and increases air temperature

Cooling

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Cooling a Data Center

• Keep temperatures within 18-27 ◦C

• Cooling equipment rated in BTUs – 1 Watt = 3412 BTUH

– BTUH = British Thermal Unit / Hour

• Keep humidity between 30-55%

– High = condensation

– Low = static shock

• Avoid hot/cold spots

– Can produce condensation

Computer Room Air Conditioning (CRAC)

• Large scale, highly reliable air conditioning units from companies like Liebert.

• Cooling capacity measured in tons.

Waterworks for Data Center

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Estimating Heat Load

Hot-Cold Aisle Architecture

• Server air intake from cold aisles

• Server air exhaust into hot aisles

• Improve efficiency by reducing mixture of hot/cold

Free Cooling

• Cooling towers dissipate heat by evaporating water, reducing or eliminating need to run chillers

• Google Belgium DC uses 100% free cooling

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Improving Cooling Efficiency

Air flow handling: Hot air exhausted by servers does not mix with cold air, and path to cooling coil is very short so little energy spent moving

Elevated cold aisle temperatures: Cold aisle of containers kept at 27◦C rather than 18-20◦C.

Use of free cooling: In moderate climates, cooling towers can eliminate majority of chiller runtime.

Server Power Usage Efficiency (SPUE)

Sources of Server Inefficiency

Primary sources of inefficiency – Power Supply Unit (PSU) (70-75% efficiency)

– Voltage Regulator Modules (VRMs) • Can lose more than 30% power in conversion losses

– Cooling fans • Software can reduce fan RPM when not needed

SPUE ratios of 1.6-1.8 are common today

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Power Supply Unit Efficiency

80 PLUS initiative to promote PSU efficiency

– 80+% efficiency at 20%, 50%, 100% of rated load

– Can be less than 80% efficient at idle power load

First 80 PLUS PSU shipped in 2005

Server Useful Power Consumption

Device Power Usage

Intel Xeon W5590 3.33 GHz Quad Core 130 W

Intel Xeon E5430 2.66 GHz Quad Core 80W

Intel Xeon E5502 2.13 GHz Dual Core 80W

7200RPM Hard Drive 7W

10,000RPM Hard Drive 14W

15,000RPM Hard Drive 20W

DDR2 DIMM 1.65W

Video Card 20-120W

The best method to determine power usage is to measure it

https://www.wattsupmeters.com/

Computation Efficiency

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Server Utilization Typically 10-50%

Figure 1. Average CPU utilization of more than 5,000 servers during a six-month period. Servers are rarely completely idle and seldom operate near their maximum utilization, instead operating most of the time at between 10 and 50 percent of their maximum

It is surprisingly hard to achieve high levels of utilization of typical servers (and your home PC is even worse)

“The Case for Energy-Proportional Computing,” Luiz André Barroso, Urs Hölzle, IEEE Computer, December 2007

Server Power Usage Range: 50-100%

Figure 2. Server power usage and energy efficiency at varying utilization levels, from idle to peak performance. Even an energy-efficient server still consumes about half its full power when doing virtually no work.

Energy efficiency = Utilization/Power

“The Case for Energy-Proportional Computing,” Luiz André Barroso, Urs Hölzle, IEEE Computer, December 2007

Server Utilization vs. Latency

Utilization 100%

Late

ncy

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Improving Power Efficiency

Improving Power Efficiency

Application consolidation – Reduce the number of applications by eliminating

old applications in favor of new ones that can server the purpose of multiple old ones.

– Allows elimination of old app servers.

Server consolidation – Use single DB for multiple applications.

– Move light services like NTP onto shared boxes.

Use SAN storage – Local disks typically highly underused

– Use SAN so servers share single storage pool

Improving Power Efficiency

Virtualization

– Host services on VMs instead of on physical servers

– Host multiple virtual servers on single physical svr

Only-as-needed Servers

– Power down servers when not in use

– Works best with cloud computing

Granular capacity planning

– Measure computing needs carefully

– Buy minimal CPU, RAM, disk configuration based on your capacity measurements and forecasts

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Key Points

Data center components – Physically secure space – Racks, the DC skeleton – Power, including UPS and PDU – Cooling – Networking

Power efficiency (server cost = 4 years power on avg) – PUE = Data center power / IT equipment power – Most power in traditional DC goes to cooling, UPS – SPUE = Server PUE; inefficiencies from PSU, VRM, fans

Cooling – Heat load estimation – Air flow control (hot/cold aisle architecture or containers) – Higher cold air temperatures (27C vs. 20C) – Free cooling (cooling towers)

References

1. Luiz Andre Barroso and Urs Holzle, The Case for Energy-Proportional Computing, IEEE Computer, Vol 40, Issue 12, December 2007.

2. Luiz Andre Barroso and Urs Holzle, The Datacenter as a Computer: An Introduction to the Design of Warehouse-Scale Machines, 1st edition, Morgan and Claypool Publishers

3. Xiaobo Fan, Wolf-Dietrich Weber, Luiz Andre Barroso, Power provisioning for a warehouse-sized computer, ISCA '07: Proceedings of the 34th annual international symposium on Computer architecture

4. Albert Greenberg, James R. Hamilton, Navendu Jain, Srikanth Kandula, Changhoon Kim, Parantap Lahiri, David A. Maltz, Parveen Patel, and Sudipta Sengupta. 2009. VL2: a scalable and flexible data center network. In Proceedings of the ACM SIGCOMM 2009 conference on Data communication (SIGCOMM '09). ACM, New York, NY, USA, 51-62.

5. Thomas A. Limoncelli, Christina J. Hogan, and Strata R. Chalup, The Practice of System and Network Administration, Second Edition, Addison-Wesley Professional, 2007.

6. Evi Nemeth, Garth Snyder, Trent R. Hein, Ben Whaley, UNIX and Linux System Administration Handbook, 4th edition, Prentice Hall, 2010.