Modeling HardDisk Power Consumption

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Modeling Hard-Disk Power Consumption

• Sumeet Sobti
• Princeton University
• Joint work with John Zedlewski, Nitin Garg,
  Fengzhou Zheng, Arvind Krishnamurthy, Randolph
  Wang

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Disk Power Simulator

• Disk simulator a program that mimics a hard-disk

Disk I/O Trace
Energy Consumption Estimate
Disk Power Simulator
Disk Parameters

• Geometry
• Performance
• Power

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Motivating Application

• Quantitative study of effects of different
  file-system attributes on energy consumption
• File-system attributes asynchrony, disk request
  re-ordering, data-layout, background
  data-reorganization,
• HUGE design space to explore
• Need a fast energy simulator

User Workload
Locality, Burstiness, Type and number of requests
Disk energy consumption
File-system Attributes
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Motivating Application (contd.)

• Simplifying assumption disk consumes power at a
  constant rate? Inaccurate.
• Not all disk activities consume equal power
• Seeking, rotation, reading, writing
• 25 difference within active periods (IBM
  Microdrive)
• Factor 10 difference in idle power (IBM
  Microdrive)
• A coarse-grained simulator may not be good enough
• LFS fewer seeks, more I/O
• Need a fine-grained energy simulator

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Related Work

• Disk Performance Modeling
• Performance simulators Ruemmler Wilkes (1994),
  Ganger, et. al. (DiskSim, 1999)
• Automatic performance parameter extraction
  Worthington et. al. (1995), Aboutabl et. al.
  (1998), Schindler Ganger (DIXTrac, 1999),
  Talagala et. al. (1999)
• Disk Power Modeling
• Douglis, et. al. (1994), Helmbold, et. al.
  (2000),
• Other applications
• Cooperative I/O Weissel, et. al. (2002),
  ECOSystem Zeng, et. al. (2002)

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Summary of Contributions

• Dempsey Fast and fine-grained disk power
  simulator
• Automatic, general techniques for extracting
  power parameters of disks
• Experimentally validated for two hard-disks
• Toshiba 5 GB PC Card Hard-Disk Drive
• IBM 1 GB Microdrive
• Evaluation of other coarse-grained power models

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The Big Picture
Disk I/O Trace
Performance Simulator (DiskSim) Energy Simulator
(Dempsey)
Performance Parameter Extractor Energy Parameter
Extractor
Geometry, Performance Parameters
Performance Profile
Energy Profile
Energy Parameters
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Dempsey Fine-grained Modeling
Seeking
Rotation
Active Energy
Reading
Writing
Total Energy
Low-Power Modes
Idle Energy
Transitions
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Active Energy Modeling

• Use DiskSim to gather statistics about disk
  stages
• Seek energy function of the seek distance
• Seek Energy Profile

energy is a linear function of
distance
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Idle and Transition Energy Modeling

• Most disks have multiple idle power modes
• Transitions between modes happen automatically
• Approximated by a table of tuples of the form
• (t, E, T)
• t length of idle period
• E energy consumed
• T additional delay introduced
• The table is easier to generate than determining
  the precise power-mode transitions
• Seems to work well in practice

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The Big Picture
Disk I/O Trace
Performance Simulator (DiskSim) Energy Simulator
(Dempsey)
Performance Parameter Extractor Energy Parameter
Extractor
Geometry, Performance Parameters
Performance Profile
Energy Profile
Energy Parameters

• Seek energy profile
• Avg. rotation power
• Avg. read power
• Avg. write power
• Idle-period energy profile

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Extracting Energy Parameters
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1
2
5
3
1 PC card extender 2 Shunt resistor 3 iPAQ
with a PCMCIA sleeve 4 PC card 5 Digital
multi-meter
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The Two-Trace Method

• To estimate avg. power for stage S, construct two
  traces that differ only in stage S.
• Rotation
• T2 sequence of write operations with large
  stride
• T1 sequence of write operations with no stride
• Reading (on disks with zero-latency access)
• T2 sequence of full track reads
• T1 sequence of SEEK commands

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Experimental Results

• Six real-world traces
• Fragments of 1992 Cello Trace from HP Labs
• 4-hour each
• Eight synthetic traces
• Small I/O, Sequential, Random, Long Idle-periods,
  Write, Cache-test
• Two disks

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Dempsey Speed and Accuracy
Toshiba HDD
Synthetic Traces
Real-world Traces
16 seconds simulation time for 24-hour long trace
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Simpler Disk Power Models

• Dempsey
• Active periods seeking, rotation, reading,
  writing
• Idle periods Idle-period energy profile
• 2-Parameter Model
• Active periods Single fixed average power
• Idle periods Single fixed average power
• 3-Parameter Model
• Active periods Single fixed average power
• Idle periods Two power modes, fixed waiting
  threshold for transition

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Simpler Disk Power Models
Toshiba HDD
Real-world Traces
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Simpler Disk Power Models
Toshiba HDD
Synthetic Traces
Long Idle-periods
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Modeling of Active Periods

• Dempsey
• Active periods seeking, rotation, reading,
  writing
• Idle periods Idle-period energy profile
• Coarse-Dempsey Model
• Active periods Single fixed average power
• Idle periods Idle-period energy profile

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Coarse-Dempsey Vs. Dempsey
Toshiba HDD
Synthetic Traces
Large Sequential Writes
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Results for IBM Microdrive
IBM Microdrive
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Conclusion

• Dempsey disk power simulator
• Speed, accuracy, generality
• Automatic, general techniques for extracting
  power parameters of disks
• Experimentally validated for two hard-disks
• Toshiba 5 GB PC Card Hard-Disk Drive
• IBM 1 GB Microdrive
• Worst observed error 7.5
• Evaluation of other coarse-grained power models