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PARAID: A Gear-Shifting Power-Aware RAID

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. Motivation. Energy costs are rising An increasing concern for servers

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PARAID: A Gear-Shifting Power-Aware RAID

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  1. PARAID:A Gear-ShiftingPower-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. 1 2 3 4 5 Soft State RAID Gears 1 2 3 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. load utilization threshold gear shift time 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. Admin Tool User Space Linux kernel File System RAID Reliability Manager PARAID Block Handler Monitor Soft RAID Disk Manager Disk Device Driver 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 PARAID: A Gear-Shifting Power-Aware RAID

  15. Data Layout • Cascading parity updates • Must also update parity in soft state 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 > threshold • Downshift (conservative) • Modified moving average + moving standard deviation < 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. client RAID USB cable P4 2.8 Ghz, 1 GB RAM 160 GB 7200 RPM SATA RAID crossover cable RAID multimeter RAID server power measurement probes Xeon 2.8 Ghz, 512 MB RAM 36.7 GB 10k RPM SCSI RAID 12v & 5v power lines BOOT SCSI cable power supply Evaluation • Measurement framework PARAID: A Gear-Shifting Power-Aware RAID

  21. Evaluation • Measurement framework 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% 64x – 550 requests/sec 128x – 1000 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 < 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 Cello99 Gear-Shifting Stats

  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> 3 disks, M gears with Gi disks within the ith gear (1 < i < M, 3 < Gi < Gi+1 < GM = D)

  40. Storage Requirement for PARAID5 Space needed for extra parity blocks S1(G1 – 1) G2 = 5 G1 = 4 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

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