Chapter 5.

Managing Storage

If there is one thing that takes up the majority of a system administrator's day, it would have to be

storage management. It seems that disks are always running out of free space, becoming overloaded

with too much I/O activity, or failing unexpectedly. Therefore, it is vital to have a solid working

knowledge of disk storage in order to be a successful system administrator.

5.1. An Overview of Storage Hardware

Before managing storage, it is first necessary to understand the hardware on which data is stored.

Unless you have at least some knowledge about mass storage devices operation, you may find yourself

in a situation where you have a storage related problem, but you lack the background knowledge

necessary to interpret what you are seeing. By gaining some insight into how the underlying hardware

operates, you will be able to more easily determine whether your computer's storage subsystem is

operating properly.

The vast majority of all mass storage devices use some sort of rotating media and supports the random

access of data on that media. This means that the following components are present in some form

within nearly every mass storage device:

Disk platters

Access arms

Data reading/writing device

The following sections explore each of these components in more detail.

5.1.1. Disk Platters

The rotating media used by nearly all mass storage devices are in the form of one or more flat,

circularly shaped platters. The platter may be composed of any number of different materials, such

aluminum, glass, and polycarbonate.

The surface of each platter is treated in such a way as to enable data storage. The exact nature of

the treatment depends on the data storage technology to be used. The most common data storage

technology is based on the property of magnetism; in these cases the platters are covered with a

compound that exhibits good magnetic characteristics.

Another common data storage technology is based on optical principles; in these cases, the platters are

covered with materials whose optical properties can be modified, thereby allowing data to be stored

optically

1

.

No matter what data storage technology is in use, the disk platters are spun, permitting their entire

surface to sweep past another component of most mass storage devices   the data reading/writing

device.

1. Some optical devices   notably CD ROM drives   use somewhat different approaches to data storage;

these differences are pointed out at the appropriate points within the chapter.