PARAID: The Gear-Shifting Power-Aware RAID

1. PARAID:The Gear-ShiftingPower-Aware RAID Charles Weddle, Mathew Oldham, An-I Andy Wang – Florida State 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 without degrading performance? The Power Aware RAID – www.cs.fsu.edu/~weddle/

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

4. Challenges • Existing Work • Most trade performance for energy savings directly. • e.g. vary speed of disks • Most are simulated results The Power Aware RAID – www.cs.fsu.edu/~weddle/

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

6. Power-Aware RAID • Skewed striping for energy savings • Preserving peak performance • Maintaining reliability • Evaluation • Conclusion • Questions The Power Aware RAID – www.cs.fsu.edu/~weddle/

7. disk 1 disk 2 disk 3 disk 4 disk 5 Soft-State Block Replication RAID Layout gear 1 gear 2 Skewed Striping for Energy Saving • Use over-provisioned spare storage • Can use fewer disks for light loads The Power Aware RAID – www.cs.fsu.edu/~weddle/

8. disk 1 disk 2 disk 3 disk 4 disk 5 Soft-State Block Replication RAID Layout gear 1 gear 2 Skewed Striping for Energy Saving • Operate in gear 1 • Disks 4 and 5 are powered off The Power Aware RAID – www.cs.fsu.edu/~weddle/

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

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

11. Preserving Peak Performance • Operate in the highest gear • When the system demands peak performance • Maximize parallelism within each gear • Load is balanced on each gear • Uniform striping pattern within each gear • Delay block replication until gear shifts • Capture block writes The Power Aware RAID – www.cs.fsu.edu/~weddle/

12. Maintaining Reliability • Distributed parity (RAID-5) • Tolerate single-disk failures • Used in soft state • Drives have a limited number of power cycles • Form bi-modal distribution of busy/idle drives • Rotate drives with more power cycles • Ration number of power cycles The Power Aware RAID – www.cs.fsu.edu/~weddle/

13. role exchange Disk 1 Disk 2 Disk 3 Disk 4 Disk 5 Disk 6 busy disks power cycled disks idle disks Gear 1 Gear 2 Gear 3 Maintaining Reliability • Busy disk stay powered on, idle disks stay powered off • Outside disks are role exchanged with middle disks The Power Aware RAID – www.cs.fsu.edu/~weddle/

14. PARAID User Administration User Space Linux kernel File System PARAID Monitor PARAID Disk Manager PARAID Reliability Manager RAID PARAID Block Handler Software RAID Disk Device Driver PARAID Implementation • Implemented in Linux 2.6.5 • ≈ 3500 lines of code The Power Aware RAID – www.cs.fsu.edu/~weddle/

15. PARAID Evaluation • Questions to answer • Can energy consumption be reduced? • Can performance be maintained? • Other questions to answer • Do the power measurements reflect workload as expected? The Power Aware RAID – www.cs.fsu.edu/~weddle/

16. 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, 2 GB RAM 36.7 GB 10k RPM SCSI RAID 12v & 5v power lines BOOT SCSI cable power supply PARAID Evaluation • Measurement framework The Power Aware RAID – www.cs.fsu.edu/~weddle/

17. PARAID Evaluation • FSU web trace workload • Obtained from Florida State University CS web servers - two months of traces • September 19 - 21, 2004, 17,000 requests • Captured web server trace files and a snapshot of the file system • No Worries, file names and content was encrypted The Power Aware RAID – www.cs.fsu.edu/~weddle/

18. Energy Savings 256x 32x 128x 64x The Power Aware RAID – www.cs.fsu.edu/~weddle/

19. Disk Utilization 256x 128x 32x 64x The Power Aware RAID – www.cs.fsu.edu/~weddle/

20. Performance – Peak Hour Latency The Power Aware RAID – www.cs.fsu.edu/~weddle/

21. Performance – Peak Hour Total Completion Time The Power Aware RAID – www.cs.fsu.edu/~weddle/

22. Postmark Benchmark • Postmark benchmark • Popular synthetic benchmark • Stresses peak read/write performance of storage device The Power Aware RAID – www.cs.fsu.edu/~weddle/

23. Conclusion • Energy efficiency and performance can be achieved simultaneously • Work in progress • Understand PARAID under a wider range of workloads. • Explore gear-centric parity schemes • Optimize gear selection and gear shifting The Power Aware RAID – www.cs.fsu.edu/~weddle/

24. Questions PARAID: The Gear-Shifting Power-Aware RAID • For more information • www.cs.fsu.edu/~weddle/ • Contact • Charles Weddle – weddle@cs.fsu.edu The Power Aware RAID – www.cs.fsu.edu/~weddle/

25. Postmark Benchmark- Total Completion Time The Power Aware RAID – www.cs.fsu.edu/~weddle/

26. Postmark BenchmarkPower – 20k Files, 100k Transactions Start in Low Gear Start in High Gear The Power Aware RAID – www.cs.fsu.edu/~weddle/