PARAID: The Gear-Shifting Power-Aware RAID Charles Weddle, Mathew Oldham, An-I Andy Wang – Florida State University RuGang Xu, Peter Reiher – University of California, Los Angeles Geoff Kuenning – Harvey Mudd College

Motivation Energy costs are rising Energy costs are rising An increasing concern for servers An increasing concern for servers No longer limited to laptops No longer limited to laptops Energy consumption of disk drives Energy consumption of disk drives 24% of the power usage in web servers 24% of the power usage in web servers 77% of the power usage in proxy servers 77% of the power usage in proxy servers 27% of operating costs for data centers 27% of operating costs for data centers The Power Aware RAID –

Challenges Energy Energy Not enough opportunities to spin down RAIDs Not enough opportunities to spin down RAIDs Performance Performance Essential for peak loads Essential for peak loads Reliability Reliability Server-class drives are not designed for frequent power switching Server-class drives are not designed for frequent power switching The Power Aware RAID –

Power-Aware RAID Observations Observations RAIDs are configured for peak performance RAIDs are configured for peak performance Uniform striping keeps all drives spinning for light loads Uniform striping keeps all drives spinning for light loads Over-provision of storage capacity Over-provision of storage capacity Unused storage can be traded for energy savings Unused storage can be traded for energy savings Cyclic fluctuation of loads Cyclic fluctuation of loads Infrequent on-off power transitions can be effective Infrequent on-off power transitions can be effective The Power Aware RAID –

Skewed Striping for Energy Saving Use over-provisioned spare storage Use over-provisioned spare storage Can use fewer drives for light loads Can use fewer drives for light loads The Power Aware RAID – gear 1 Soft-State Block Replication gear 2 disk 1disk 2disk 3disk 4 gear 3 RAID-5 Layout

Preserving Peak Performance Based on RAID-5 Based on RAID-5 All drives on for peak loads All drives on for peak loads Full parallelism Full parallelism Fewer drives on for light loads Fewer drives on for light loads Lower latency for small files Lower latency for small files Degraded throughput for large files Degraded throughput for large files The Power Aware RAID –

Reliability Drives have a limited number of power cycles Drives have a limited number of power cycles Form bi-modal distribution of busy/idle drives Form bi-modal distribution of busy/idle drives Rotate drives with more power cycles Rotate drives with more power cycles Ration number of power cycles Ration number of power cycles Distributed parity (RAID-5) Distributed parity (RAID-5) Tolerate single-disk failures Tolerate single-disk failures The Power Aware RAID –

PARAID-0 Webserver Tests The Power Aware RAID –

WIP & Conclusion Moving from PARAID-0 to PARAID-5 Moving from PARAID-0 to PARAID-5 Exploring different server loads Exploring different server loads Energy efficiency and performance can be achieved simultaneously Energy efficiency and performance can be achieved simultaneously PARAID-0 with “2 gears” has already shown a 15% reduction in power with < 1% performance loss PARAID-0 with “2 gears” has already shown a 15% reduction in power with < 1% performance loss The Power Aware RAID –

Questions PARAID: The Gear-Shifting Power-Aware RAID For More Information For More Information Contact Contact Charles Weddle – Charles Weddle – The Power Aware RAID –