A Hybrid Disk-Aware Spin-Down Algorithm with I/O Subsystem Support


  A Hybrid Disk-Aware Spin-Down Algorithm.pdf (Size: 549.5 KB / Downloads: 0)


Abstract

To offset the significant power demands of hard disk
drives in computer systems, drives are typically powered
down during idle periods. This saves power, but accelerates
duty cycle consumption, leading to earlier drive failure.
Hybrid disks with a small amount of non-volatile
flash memory (NVCache) are coming on the market.

Introduction

Hard disks consume a significant amount of power. In
general purpose computing, hard disks can be responsible
for as much as 30% of a system’s power consumption
[12, 16]. This percentage will only increase as current
CPU trends lean toward increasing the number of cores versus
the single core clock rate [11], hard disks use faster rotational
speeds, and multiple hard disks per (desktop) system
become more prevalent. In large storage systems, hard
disks can dominate system power consumption: 86% [1]
and 71% [2] of the total power consumption in EMC and
Dell storage servers, respectively.

Hybrid Disk Overview

We now present an overviewof a hybrid disk and how its
NVCache can be managed by a host operating system using
a modified set of ATA commands, according to the T13
specification for hybrid disks [19]. The four enhancements
are presented in Section 3. Sectors stored in the NVCache
are either pinned or unpinned, which when referred to as
a collection are known as the pinned and unpinned set, respectively.
The host manages the pinned set, while the disk
manages the unpinned set.

Hybrid Disk-Aware Spin-Down Algorithm
with I/O Subsystem Support

Spin-down algorithms which control the power state of
traditional hard disks are efficient at reducing disk power
consumption. There is little room for improvement of such
algorithms, which dynamically adjust to the most powerefficient
time-out using machine learning techniques [13].
Hybrid disks present an opportunity for spin-down algorithms
to further reduce power consumption while minimizing
the performance and reliability impact they impose
on the media itself. We now describe four spin-down algorithm
and I/O subsystem enhancements.