PARAID: The Gear-Shifting Power-Aware RAID

PARAID:PARAID:The The Gear-ShiftingGear-Shifting

Power-Aware RAIDPower-Aware RAIDCharles Weddle, Mathew Oldham, An-I Andy Wang – Florida State UniversityCharles Weddle, Mathew Oldham, An-I Andy Wang – Florida State University

Peter Reiher – University of California, Los AngelesPeter Reiher – University of California, Los Angeles

Geoff Kuenning – Harvey Mudd CollegeGeoff Kuenning – Harvey Mudd College

MotivationMotivation Energy costs are risingEnergy costs are rising

An increasing concern for serversAn increasing concern for servers No longer limited to laptopsNo longer limited to laptops

Energy consumption of disk drivesEnergy consumption of disk drives 24% of the power usage in web servers24% of the power usage in web servers 27% of electricity cost for data centers27% of electricity cost for data centers Root to other issues, e.g. server room coolingRoot to other issues, e.g. server room cooling

Is it possible to reduce energy consumption Is it possible to reduce energy consumption without degrading performance?without degrading performance?

The Power Aware RAID – www.cs.fsu.edu/~weddle/

ChallengesChallenges EnergyEnergy

Not enough opportunities to spin down RAIDsNot enough opportunities to spin down RAIDs

PerformancePerformance Essential for peak loadsEssential for peak loads

ReliabilityReliability Server-class drives are not designed for Server-class drives are not designed for

frequent power switchingfrequent power switching


ChallengesChallenges Existing WorkExisting Work

Most trade performance for energy savings Most trade performance for energy savings directly. directly. e.g. vary speed of diskse.g. vary speed of disks

Most are simulated resultsMost are simulated results


ObservationsObservations Over provisioning of resourcesOver provisioning of resources

RAID is configured for peak performanceRAID is configured for peak performance RAID keeps all drives spinning for light loadsRAID keeps all drives spinning for light loads

Unused storage capacityUnused storage capacity Over-provision of storage capacityOver-provision of storage capacity Unused storage can be traded for energy savingsUnused storage can be traded for energy savings

Fluctuating loadFluctuating load Cyclic fluctuation of loadsCyclic fluctuation of loads Infrequent on-off power transitions can be effectiveInfrequent on-off power transitions can be effective


Power-Aware RAIDPower-Aware RAID Skewed striping for energy savingsSkewed striping for energy savings Preserving peak performancePreserving peak performance

Maintaining reliabilityMaintaining reliability

EvaluationEvaluation ConclusionConclusion QuestionsQuestions


Skewed StripingSkewed Striping for Energy Saving for Energy Saving Use over-provisioned spare storageUse over-provisioned spare storage Can use fewer disks for light loadsCan use fewer disks for light loads


gear 1

Soft-State Block

Replication

disk 1

gear 2

RAID Layout

disk 2 disk 3 disk 4 disk 5

Skewed StripingSkewed Striping for Energy Saving for Energy Saving Operate in gear 1Operate in gear 1 Disks 4 and 5 are powered offDisks 4 and 5 are powered off


gear 1

Soft-State Block

Replication

disk 1

gear 2

RAID Layout

disk 2 disk 3 disk 4 disk 5

Skewed StripingSkewed Striping for Energy Saving for Energy Saving Approximate the workloadApproximate the workload Gear shift into most appropriate gearGear shift into most appropriate gear

Minimize the opportunity lost to save powerMinimize the opportunity lost to save power


Energy( PoweredOn Disks )

Workload( Disk Parallelism )

Conventional RAID PARAID

workload

Skewed StripingSkewed Striping for Energy Saving for Energy Saving Adapt to cyclic fluctuating workloadAdapt to cyclic fluctuating workload Gear shift when gear utilization threshold is metGear shift when gear utilization threshold is met


time

load

utilization threshold

gear shift

Preserving Peak PerformancePreserving Peak Performance Operate in the highest gear Operate in the highest gear

When the system demands peak performanceWhen the system demands peak performance

Maximize parallelism within each gearMaximize parallelism within each gear Load is balanced on each gearLoad is balanced on each gear Uniform striping pattern within each gearUniform striping pattern within each gear

Delay block replication until gear shiftsDelay block replication until gear shifts Capture block writesCapture block writes


Maintaining ReliabilityMaintaining Reliability Distributed parity (RAID-5)Distributed parity (RAID-5)

Tolerate single-disk failuresTolerate single-disk failures Used in soft stateUsed in soft state

Drives have a limited number of power Drives have a limited number of power cyclescycles Form bi-modal distribution of busy/idle drivesForm bi-modal distribution of busy/idle drives Rotate drives with more power cyclesRotate drives with more power cycles Ration number of power cyclesRation number of power cycles


Maintaining ReliabilityMaintaining Reliability Busy disk stay powered on, idle disks stay powered offBusy disk stay powered on, idle disks stay powered off Outside disks are role exchanged with middle disksOutside disks are role exchanged with middle disks


busydisks

powercycleddisks

idledisks

role exchange

Disk 1

Gear 1Gear 2

Gear 3

Disk 2 Disk 3 Disk 4 Disk 5 Disk 6

PARAID ImplementationPARAID Implementation Implemented in Linux 2.6.5 Implemented in Linux 2.6.5 ≈≈ 3500 lines of code3500 lines of code


File System

RAID

PARAID Block Handler

Disk Device Driver

PARAID User Administration

PARAID Monitor

PARAID Disk

Manager

PARAID Reliability Manager

User Space

Linux kernel

Software RAID

PARAID EvaluationPARAID Evaluation

Questions to answerQuestions to answer Can energy consumption be reduced?Can energy consumption be reduced? Can performance be maintained?Can performance be maintained?

Other questions to answerOther questions to answer Do the power measurements reflect workload Do the power measurements reflect workload

as expected?as expected?


PARAID EvaluationPARAID Evaluation

Measurement frameworkMeasurement framework


multimeter

USB cableclient

server

powersupply

12v & 5vpower lines

powermeasurement

probes

SCSIcable

crossover cable

Xeon 2.8 Ghz, 2 GB RAM36.7 GB 10k RPM SCSI

P4 2.8 Ghz, 1 GB RAM160 GB 7200 RPM SATA

RAID

RAID

RAID

RAID

RAID

BOOT

PARAID EvaluationPARAID Evaluation FSU web trace workloadFSU web trace workload

Obtained from Florida State University CS web servers - two months of tracesObtained from Florida State University CS web servers - two months of traces September 19 - 21, 2004, 17,000 requestsSeptember 19 - 21, 2004, 17,000 requests Captured web server trace files and a snapshot of the file systemCaptured web server trace files and a snapshot of the file system No Worries, file names and content was encryptedNo Worries, file names and content was encrypted


Energy SavingsEnergy Savings


256x

128x

64x

32x

Speed-UpSpeed-Up Energy SavingsEnergy Savings

256x256x 3.3%3.3%

128x128x 1.2%1.2%

64x64x 12%12%

32x32x 19%19%

Disk UtilizationDisk Utilization


256x

128x

64x

32x

Performance – Peak Hour LatencyPerformance – Peak Hour Latency

RAID 5RAID 5 PARAIDPARAID

256x256x 85%85% 76%76%

126x126x 79%79% 83%83%

64x64x 87%87% 88%88%

32x32x 92%92% 92%92%


Performance – Peak Hour Total Completion TimePerformance – Peak Hour Total Completion Time

RAID 5RAID 5 PARAIDPARAID

256x256x 79%79% 71%71%

128x128x 75%75% 78%78%

64x64x 81%81% 81%81%

32x32x 87%87% 86%86%


Postmark BenchmarkPostmark Benchmark

Postmark benchmarkPostmark benchmark Popular synthetic benchmarkPopular synthetic benchmark Stresses peak read/write performance of storage Stresses peak read/write performance of storage

devicedevice


ConclusionConclusion Energy efficiency and performance can be Energy efficiency and performance can be

achieved simultaneouslyachieved simultaneously Work in progressWork in progress

Understand PARAID under a wider range of Understand PARAID under a wider range of workloads.workloads.

Explore gear-centric parity schemesExplore gear-centric parity schemes

Optimize gear selection and gear shiftingOptimize gear selection and gear shifting


QuestionsQuestions

PARAID: PARAID: The The Gear-ShiftingGear-Shifting Power-Aware RAIDPower-Aware RAID

For more informationFor more information www.cs.fsu.edu/~weddle/www.cs.fsu.edu/~weddle/

ContactContact Charles Weddle – [email protected] Weddle – [email protected]


http://www.cs.fsu.edu/~weddle/

Postmark Benchmark- Total Completion TimePostmark Benchmark- Total Completion Time


RAID 5RAID 5 PARAID PARAID High High GearGear

PARAID PARAID Low Low GearGear

1k Files,1k Files,50k Trans50k Trans

5s5s 6s6s 4.8s4.8s

20k Files,20k Files,50k Trans50k Trans

64.8s64.8s 58.8s58.8s 130.4s130.4s

20k Files,20k Files,100kTrans100kTrans

147.8s147.8s 136.2s136.2s 261.2s261.2s

Postmark BenchmarkPostmark BenchmarkPower – 20k Files, 100k TransactionsPower – 20k Files, 100k Transactions


Start in High Gear Start in Low Gear

PARAID: The Gear-Shifting Power-Aware RAID

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