Fred Chong 290N Green Computing Datacenter Basics Fred Chong 290N Green Computing

Figure : Storage hierarchy of a Warehouse-scale computer

Performance Variations Figure : Latency, bandwidth and capacity of a Warehouse-scale computer

Server Comparison HP Integrity Superdome – Itanium2 HP ProLiant ML350 G5 Processor 64 sockets, 128 cores (dual- threaded), 1.6GHz Itanium2, 12MB last-level cache 1 socket, quad-core, 2.66GHz X5355 CPU, 8MB last-level cache Memory 2048GB 24GB Disk storage 320,974GB, 7056 drives 3961GB, 105 drives TPC-C price/perfor mance $2.93/tpmC $0.73/tpmC price/perfor mance (server HW only) $1.28/transactions per minute $0.10/transactions per minute price/perfor mance (server HW only) (no discounts) $2.39/transactions per minute $0.12/transactions per minute

Cost proportional to Power Cost proportional to power delivered Typically $10-20/W Power delivery 60-400kV transmission lines 10-20kV medium voltage 110-480V low voltage

UPS Uninterruptible Power Supply Batteries or flywheel AC-DC-AC conversion Conditions the power feed Removes spikes or sags Removes harmonic distortions Housed in a separate UPS room Sizes range from hundreds of kW to 2MW

PDUs Power Distribution Units Breaker panels Input 200-480V Output many 110V or 220V 75-225kW in 20-30A circuits (max 6 kW) Redundancy from two independent power sources

Paralleling Multiple generators or UPSs N+1 (one failure) Feed a shared bus N+1 (one failure) N+2 (one maintenance, one failure) 2N (redundant pairs)

Cooling

Cooling Steps 12-14 C coolant 16-20 C air at CRAC (Computer Room AC) 18-22 C at server intake Then back to chiller

“Free Cooling” Pre-cool coolant before chiller Water-based cooling towers use evaporation Works in moderate climate – freezes if too cold Glycol-based radiator outside the building Works in cold climates

Cooling is Critical Datacenter would fail in minutes without cooling Cooling backed up by generators and UPSs Adds > 40% critical electrical load

Airflow 100 cfm (cubic feet per minute) per server 10 servers would require 1000 cfm from perforated tiles Typically no more than 150-200W / sq ft power density Recirculation from one server’s hot air into the intake of a neighbor Some avoid with overhead ducts

Variations In-rack cooling Container-based datacenters Water cooled coils next on the server Cost of plumbing Damage from leaks (earthquake zones!) Container-based datacenters Shipping container 8’ x 8.5’ x 40’ Similar to in-rack cooling but for the whole container Higher power densities

Power Efficiency PUE – power usage efficiency Datacenter power infrastructure

Poor PUEs 85% of datacenters PUE > 3 Only 5% PUE = 2.0 Chillers take 30-50% overhead CRAC 10-30% overhead UPS 7-12% overhead (AC-DC-AC) Humidifiers, PDUs, lighting EPA “achievable” PUE of 1.4 by 2011

Improvements Evaporative cooling Efficient air movement Eliminate power conversion losses Google PUE = 1.21 Several companies PUE = 1.3

A more comprehensive metric (b) SPUE – server power usage efficiency (c) computation energy efficiency

SPUE Power delivered to components directly involved in computation: Motherboad, disks, CPUs, DRAM, I/O cards Losses due to power supplies, fans, voltage regulators SPUE of 1.6-1.8 common Power supplies less than 80% efficient Voltage regulators less than 70% efficient EPA feasible SPUE < 1.2 in 2011

TPUE Total PUE = TPUE = PUE * SPUE Average of 3.2 today (2.2 Watts wasted for every Watt in computation) PUE 1.2 and SPUE 1.2 would give 2X benefit TPUE of 1.25 probably the limit of what is economically feasible

Computing Efficiency Area of greatest potential Hardest to measure SPECpower Joulesort Storage Network Industry Association

SPECPower Example

Server Load

Load vs Efficiency

Human Dynamic Range

Component Efficiency

CPU Voltage Scaling

Disks As much as 70% power to keep drives spinning 1000X penalty to spin up and access Multiple head, low RPM drives [Gurumurthi]

Server Power Supplies

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

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

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