Lecture 4 power provisioning
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Lecture 4: Power Provisioning. Prof. Fred Chong 290N Green Computing. Power Provisioning. $10-22 per deployed IT Watt Given 10 year depreciation cycle $1-2.20 per Watt per year Assume $0.07 per kilowatt-hr and PUE 2.0 8766 hours in a year (8766 / 1000) * $0.07 * 2.0 = $1.22724

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Lecture 4: Power Provisioning

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Lecture 4: Power Provisioning

Prof. Fred Chong

290N Green Computing


Power Provisioning

  • $10-22 per deployed IT Watt

  • Given 10 year depreciation cycle

    • $1-2.20 per Watt per year

  • Assume $0.07 per kilowatt-hr and PUE 2.0

    • 8766 hours in a year

    • (8766 / 1000) * $0.07 * 2.0 = $1.22724

  • Up to 2X cost in provisioning

    • eg. 50% full datacenter = 2X provisioning cost


Power Distribution Revisited


Measured Load vs Power


Modeled vs. Measured PDU Power


Methodology


Workloads

  • Websearch – high request throughput and large data size

  • Webmail – high I/O

  • Mapreduce – large offline batch jobs


Websearch Results


Webmail Results


Mapreduce Results


Mixed Load


Real Datacenter


Time at Power Level

80 servers

800 servers

8000 servers


Oversubscription Opportunity

  • 7% for racks (80)

  • 22% for PDUs (800)

  • 28% for clusters (8000)

    • Could have hosted almost 40% more machines


Power Capping


Observed Power


CPU DVS


Idle Power


Energy Savings


Underdeployment

  • New facilities plan for growth

  • Also discretization of capacity

    • Eg 2.5kW circuit may have four 520W servers

      • 17% underutilized, but can’t have one more


Modeling Costs

TCO =datacenter depreciation + datacenter opex +server depreciation + server opex


$ per critical watt


Case A

  • Dell 2950 III EnergySmart

    • 16GB of RAM and 4 disks

    • 300 Watts

    • $6K


Assumptions

  • The cost of electricity is the 2006 average US industrial rate ay 6.2 cents/kWh.

  • The interest rate a business must pay on their loans is 12%.

  • The cost of datacenter construction is $15/W amortized over 12 years.

  • Datacenter opex is $0.03/W/month.

  • The datacenter has a PUE of 2.0.

  • Server lifetime is 4 years, and server repair and maintenance is 5% of capex per year.

  • The server’s average power draw is 75% of peak power.


Cost Breakdown A


Case B

  • higher-powered server

    • 500W

    • $2K

  • energy cost of $0.10/kWh

  • datacenter related costs rise to 46% of the total

  • energy costs to 25%

  • server costs falling to 31%.

  • hosting cost of such a server, i.e., the cost of all infrastructure and power to house it, is more than twice the cost of purchasing and maintaining the server.


Cost Breakdown B


Utilization

  • CPU Utilization of 50% => 75% Peak Power

  • Nameplate 500W server

    • with all options (max mem, disk, PCI cards)

    • but more commonly 300W

    • Thus 60% utilized => 1.66x OPEX

  • Vendor power calculator assumes 100% CPU utilization


Power Provisioning Problems

  • Assume 30% CPU utilization and provision power accordingly

    • 200W instead of 300W

    • Variations could cause server to overhead or trip a breaker

    • Adding memory or disk would require physical decompaction of racks

  • Thus 20-50% slack space common

    • Eg 10MW provisioned power => 4-6 MW actual power (plus PUE overhead)


Case B with 50% Occupancy


Partial Utilization Costs

  • Partially utilized servers use less power

    • Appear to cost less in OPEX cost per server

    • But produce less value in terms of applications

  • Need metric for application value

    • Eg number of transactions, number of web searches

    • Divide TCO by metric

    • Eg TCO = $1M/month, 100M transactions/month => 1 cent / transaction

    • Eg TCO = $1M/month, 50M transactions/month => 2 cents / transaction (2X cost)


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