Managing RAID on Linux

Chapter 1. Introduction

Every system administrator sooner or later realizes that the most elusive foe in sustaining reliable system performance is bandwidth. On one hand, network connectivity provides a crucial connection to the outside world through which your servers deliver data to users. This type of bandwidth, and its associated issues, is well documented and well studied by virtually all system and network administrators. It is at the forefront of modern computing, and the topic most often addressed by both non-technical managers and the mainstream media. A multitude of software and documentation has been written to address network and bandwidth issues. Most administrators, however, don’t realize that similar bandwidth problems exist at the bus level in each system you manage. Unfortunately, this internal data transfer bottleneck is more sparsely documented than its network counterpart. Because of its second stage coverage, many administrators, users, and managers are left with often perplexing performance issues.

Although we tend to think of computers as entirely electronic, they still rely on moving parts. Hard drives, for example, contain plates and mechanical arms that are subject to the constraints of the physical world we inhabit. Introducing moving parts into a digital computer creates an inherent bottleneck. So even though disk transfer speeds have risen steadily in the past two decades, disks are still an inherently slow component in modern computer systems. A high-performance ...