``Caching for Bursts (C-Burst): let hard disks sleep well and work 

Feng Chen and Xiaodong Zhang 

Proceedings of 13th ACM/IEEE International Symposium on Low Power
Electronics and Design (ISLPED'08), Bangalore, India, August 11-13,


High energy consumption has become a critical challenge in all kinds of 
computer systems. Hardware-supported Dynamic Power Management (DPM) 
provides a mechanism to save disk energy by transitioning an idle disk 
to a low-power mode. However, the achievable disk energy saving is mainly 
dependent on the pattern of I/O requests received at the disk.
In particular, for a given number of requests, a bursty disk access 
pattern serves as a foundation for energy optimization. Aggressive 
prefetching has been used to increase disk access burstiness and extend 
disk idle intervals, while caching, a critical component in buffer cache 
management, has not been paid a specific attention. In the absence of 
cooperation from caching, the attempt to create bursty disk accesses would 
often be disturbed due to improper replacement decision made by energy-unaware 
caching policies. In this paper, we present the design of a set of 
comprehensive energy-aware caching schemes, called C-Burst, and its 
implementation in Linux kernel 2.6.21. Our caching schemes leverage the 
`filtering' effect of buffer cache to effectively reshape the disk access 
stream to a bursty pattern for energy saving. The experiments under 
various scenarios show that C-Bursts chemes can achieve up to 35% disk 
energy saving with minimal performance loss.