Sensitivity-Based Optimization of Disk Architecture

Many applications, especially those that run on servers, are I/O intensive and therefore require high-performance storage systems. These high-end storage systems consume a large amount of power, the bulk of which is due to the disk drives. Optimizing disk architectures is a design-time, as well as a run-time, issue, and requires performance and power trade-offs. A hard disk designer needs to balance between the disk rotational speed (rotations per minute, RPM), platter sizes, and the number of platters. The RPM and platter sizes affect performance, and all three have an impact on power. A data center manager might have specific energy budgets within which she has to extract as much performance as possible. Applications themselves may have specific optimization requirements. Therefore, there are different figures of merit, such as performance and energy, and a large space of design and runtime "knobs" that can be used to optimize disk drive behavior. Given such a large space, it is desirable to have a systematic methodology to optimally set these knobs to satisfy the figures of merit as efficiently as possible. In this paper, we present the Sensitivity-based Optimization methodology for Disk Architectures (SODA), which leverages results previously obtained in digital circuit design optimization scenarios. Using detailed models of the electromechanical behavior of disk drives, and a suite of realistic workloads, we show how SODA can aid in design and runtime optimization of disk drive architectures.