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PARAID: A Gear-Shifting Power-Aware RAID

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PARAID: A Gear-Shifting Power-Aware RAID Charles Weddle, Mathew Oldham, Jin Qian, An-I Andy Wang Florida St. University Peter Reiher University of California ... – PowerPoint PPT presentation

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Title: PARAID: A Gear-Shifting Power-Aware RAID


1
PARAID A Gear-Shifting Power-Aware RAID
  • Charles Weddle, Mathew Oldham, Jin Qian, An-I
    Andy Wang Florida St. University
  • Peter Reiher University of California, Los
    Angeles
  • Geoff Kuenning Harvey Mudd College

2
Motivation
  • Energy costs are rising
  • An increasing concern for servers
  • No longer limited to laptops
  • Energy consumption of disk drives
  • 24 of the power usage in web servers
  • 27 of electricity cost for data centers
  • Root to other issues, e.g. server room cooling
  • Is it possible to reduce energy consumption in
    RAID devices without degrading performance while
    maintaining reliability?

PARAID A Gear-Shifting Power-Aware RAID
3
Challenges
  • Energy
  • Not enough opportunities to spin down RAIDs
  • Performance
  • Essential for peak loads
  • Reliability
  • Server-class drives are not designed for frequent
    power switching

PARAID A Gear-Shifting Power-Aware RAID
4
Existing Work
  • Most trade performance for energy savings
    directly.
  • For example, vary the speed of disks
  • Most are simulated results

PARAID A Gear-Shifting Power-Aware RAID
5
Observations
  • Over provisioning of resources
  • RAID is configured for peak performance
  • RAID keeps all drives spinning for light loads
  • Unused storage capacity
  • Over-provision of storage capacity
  • Unused storage can be traded for energy savings
  • Fluctuating load
  • Cyclic fluctuation of loads
  • Infrequent on-off power transitions can be
    effective

PARAID A Gear-Shifting Power-Aware RAID
6
Power-Aware RAID
  • Skewed striping for energy savings
  • Preserving peak performance
  • Maintaining reliability
  • Evaluation
  • Conclusion
  • Questions

PARAID A Gear-Shifting Power-Aware RAID
7
Skewed Striping for Energy Saving
  • Use over-provisioned spare storage
  • Can use fewer disks for light loads

PARAID A Gear-Shifting Power-Aware RAID
8
Skewed Striping for Energy Saving
  • Operate in gear 1
  • Disks 4 and 5 are powered off

1
2
3
4
5
Soft State
RAID
Gears
1
2
3
PARAID A Gear-Shifting Power-Aware RAID
9
Skewed Striping for Energy Saving
  • Approximate the workload
  • Gear shift into most appropriate gear
  • Minimize the opportunity lost to save power

Conventional RAID
PARAID
Energy ( Powered On Disks )
workload
Workload ( Disk Parallelism )
PARAID A Gear-Shifting Power-Aware RAID
10
Skewed Striping for Energy Saving
  • Adapt to cyclic fluctuating workload
  • Gear shift when gear utilization threshold is met

PARAID A Gear-Shifting Power-Aware RAID
11
Preserving Peak Performance
  • Operate in the highest gear
  • When the system demands peak performance
  • Uses the same disk layout
  • Maximize parallelism within each gear
  • Load is balanced on each gear
  • Uniform striping pattern within each gear
  • Delay block replication until gear shifts
  • Track block writes as an optimization

PARAID A Gear-Shifting Power-Aware RAID
12
Maintaining Reliability
  • Reuse existing RAID levels (RAID-5)
  • Also used in soft state
  • Drives have a limited number of power cycles
  • Ration number of power cycles

PARAID A Gear-Shifting Power-Aware RAID
13
Logical Component Design
PARAID A Gear-Shifting Power-Aware RAID
14
Data Layout
  • Parity for 5 disks does not work for 4 disks
  • For example, replicated block 12 on disk 3

Disk 1 Disk 2 Disk 3 Disk 4 Disk 5
Soft State (RAID-5) (1-4) 8 12 ((1-4),8,12)
Soft State (RAID-5) 16 20 (16,20,_) _
RAID-5 1 2 3 4 (1-4)
RAID-5 5 6 7 (5-8) 8
RAID-5 9 10 (9-12) 11 12
RAID-5 13 (13-16) 14 15 16
RAID-5 (17-20) 17 18 19 20
PARAID A Gear-Shifting Power-Aware RAID
15
Data Layout
  • Cascading parity updates
  • Must also update parity in soft state

Disk 1 Disk 2 Disk 3 Disk 4 Disk 5
Soft State (RAID-5) (1-4) 8 12 ((1-4),8,12)
Soft State (RAID-5) 16 20 (16,20,_) _
RAID-5 1 2 3 4 (1-4)
RAID-5 5 6 7 (5-8) 8
RAID-5 9 10 (9-12) 11 12
RAID-5 13 (13-16) 14 15 16
RAID-5 (17-20) 17 18 19 20
PARAID A Gear-Shifting Power-Aware RAID
16
Update Propagation
  • Up-shift propagation
  • Full synchronization
  • On-demand synchronization
  • For example, shifting from 3 to 5 disks
  • Downshift propagation
  • Full synchronization

PARAID A Gear-Shifting Power-Aware RAID
17
Asymmetric Gear-Shifting Policies
  • Up-shift (aggressive)
  • Moving average moving standard deviation gt
    threshold
  • Downshift (conservative)
  • Modified moving average moving standard
    deviation lt threshold
  • Moving average modified to account for extra
    parity updates

PARAID A Gear-Shifting Power-Aware RAID
18
Implementation
  • Prototyped in Linux 2.6.5
  • Open source, software RAID
  • Implemented block I/O handler, monitor, disk
    manager
  • Implemented user admin tool to configure device
  • Updated Raid Tools to recognize PARAID level

PARAID A Gear-Shifting Power-Aware RAID
19
Evaluation
  • Challenges
  • Prototyping PARAID
  • Commercial machines
  • Benchmarks are designed to measure peak
    performance
  • Trace replay
  • Time consuming

PARAID A Gear-Shifting Power-Aware RAID
20
Evaluation
  • Measurement framework

PARAID A Gear-Shifting Power-Aware RAID
21
Evaluation
  • Measurement framework

  Server Client
Processor Intel Xeon 2.8 Ghz Intel Pentium 4 2.8 Ghz
Memory 512 Mbytes 1 Gbytes
Network Gigabit Ethernet Gigabit Ethernet
Disks 36.7Gbytes 15K RPM SCSI Ultra 320 160 Gbytes 7200 RPM SATA
PARAID A Gear-Shifting Power-Aware RAID
22
Evaluation
  • Three different workloads using two different
    RAID settings
  • Web trace - RAID level 0 2 gears (2,5)
  • Mostly read activity
  • Cello99 - RAID level 5 2 gears (3,5)
  • I/O intensive workload with writes
  • Postmark - RAID level 5 2 gears (3,5)
  • Measure peak performance and gear shifting
    overhead
  • Speed up trace playback
  • To match hardware
  • Explore range of speed up factors and power
    savings

PARAID A Gear-Shifting Power-Aware RAID
23
Web Trace
  • UCLA CS Dept Web Servers (8/11/2006 8/14/2006)
  • File system 32 GB (500k files)
  • Trace replay 95k requests with 4 GB data (260
    MB unique)

PARAID A Gear-Shifting Power-Aware RAID
24
Web Trace Energy Savings
64x 60 requests/sec
Energy Savings
64x - 34
128x - 28
256x - 10
128x 120 requests/sec
256x 240 requests/sec
PARAID A Gear-Shifting Power-Aware RAID
25
Web Trace Latency
256x
Overhead
256x - within 2.7
64x - 240 80ms vs. 33ms
128x
64x
PARAID A Gear-Shifting Power-Aware RAID
26
Web Trace Bandwidth
256x
Overhead
256x - within 1.3 in high gear
128x
64x
PARAID A Gear-Shifting Power-Aware RAID
27
Cello99 Trace
  • Cello99 Workload
  • HP Storage Research Labs
  • 50 hours beginning on 9/12/1999
  • I/O intensive with 42 writes

PARAID A Gear-Shifting Power-Aware RAID
28
Cello99 Energy Savings
32x 270 requests/sec
Energy Savings
32x - 13
64x - 8.2
128x - 3.5
128x 1000 requests/sec
64x 550 requests/sec
PARAID A Gear-Shifting Power-Aware RAID
29
Cello99 Completion Time
128x
Overhead
32x - 1.8ms, 26 slower due to time spent in
low gear
64x
32x
PARAID A Gear-Shifting Power-Aware RAID
30
Cello99 Bandwidth
128x
Overhead
lt 1 degra- dation during peak hours
64x
32x
PARAID A Gear-Shifting Power-Aware RAID
31
Postmark Benchmark
  • Popular synthetic benchmark
  • Generates ISP-style workloads
  • Stresses peak read/write performance of storage
    device

PARAID A Gear-Shifting Power-Aware RAID
32
Postmark Performance
PARAID A Gear-Shifting Power-Aware RAID
33
Postmark Power Measurements
PARAID A Gear-Shifting Power-Aware RAID
34
Ongoing Work
  • Try more workloads
  • Optimize PARAID gear configuration
  • Explore asynchronous update propagation
  • Speed up recovery
  • Live testing

PARAID A Gear-Shifting Power-Aware RAID
35
Lessons Learned
  • Third version of design, early design not
    portable
  • Data alignment problems
  • Difficult to measure system under normal load
  • Hardware and operating system optimizations
  • Matching trace environment

PARAID A Gear-Shifting Power-Aware RAID
36
Conclusion
  • PARAID reuses standard RAID-levels without
    special hardware while decreasing their energy
    use by 34.
  • Optimized version can save even more energy
  • Empirical evaluation important

PARAID A Gear-Shifting Power-Aware RAID
37
Questions
PARAID A Gear-Shifting Power-Aware RAID
38
PARAID Gear-Shifting
Web Trace Gear-Shifting Stats
256x 128x 64x
Number of gear switches 15.2 8.0 2.0
time spent in low gear 52 88 98
extra I/Os for update propagations 0.63 0.37 0.21
Cello99 Gear-Shifting Stats
128x 64x 32x
Number of gear switches 6.0 5.6 5.4
time spent in low gear 47 74 88
extra I/Os for update propagations 8.0 15 21
39
Storage Requirement for PARAID5
Storage consumption Si for the total RAID for the
ith gear
  • PARAID uses around (D G1)/(D 1) of the total
    RAID-5 storage to store soft states.
  • For RAID-5, D gt 3 disks, M gears with Gi disks
    within the ith gear (1 lt i lt M, 3 lt Gi lt Gi1 lt
    GM D)

40
Storage Requirement for PARAID5
Space needed for extra parity blocks
S1(G1 1)
G2 5
G1 4
Disk 1 Disk 2 Disk 3 Disk 4 Disk 5
Gear 1 RAID-5 (1-4) 8 12 ((1-4),8,12)
Gear 1 RAID-5 16 20 (16,20,_) _
Gear 2 RAID-5 1 2 3 4 (1-4)
Gear 2 RAID-5 5 6 7 (5-8) 8
Gear 2 RAID-5 9 10 (9-12) 11 12
Gear 2 RAID-5 13 (13-16) 14 15 16
Gear 2 RAID-5 (17-20) 17 18 19 20
S1
S2
S1 S2 1
S1(G1 1) S2(G2 G1)
S2(G2 G1)
41
PARAID
Target percentage energy savings
  • Energy savings increase with more disks and
    fewer disks in the lowest gear.
  • A higher active/standby ratio.
  • D the number of disks in the array
  • G1 the disks in gear 1.
  • P power in standby/active/idle

42
PARAID
Modified moving utilization
  • Accounts for cascading parity writes in lower
    gear.
  • Gi the disks in gear i.
  • Aread/write the read or write activity
  • W the weight to account for additional parity
    writes
  • (RAID5 1.5)

43
PARAID
max min configuration empty storage max energy savings formula
4 3 3-4 33.00 25.00 0.333333
5 3 3-5 50.00 40.00 0.5
5 4 4-5 25.00 20.00 0.25
5 3 3-4-5 50.00 40.00 0.5
6 3 3-6 60.00 50.00 0.6
6 4 4-6 40.00 33.00 0.4
6 5 5-6 20.00 17.00 0.2
6 3 3-4-6 60.00 50.00 0.6
6 3 3-5-6 60.00 50.00 0.6
6 4 4-5-6 40.00 33.00 0.4
6 3 3-4-5-6 60.00 50.00 0.6
7 3 3-7 66.67 57.14 0.666667
7 4 4-7 50.00 42.86 0.5
7 5 5-7 33.00 28.57 0.333333
7 6 6-7 16.67 14.29 0.166667
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