Red Hat ENTERPRISE LINUX 5 - VIRTUAL SERVER ADMINISTRATION, Руководство по установке

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Chapter 26. An Introduction to Disk Partitions
264
As
Figure 26.2, “Disk Drive with a File System”
, implies, the order imposed by a file system involves
some trade-offs:
• A small percentage of the drive's available space is used to store file system-related data and can
be considered as overhead.
• A file system splits the remaining space into small, consistently-sized segments. For Linux, these
segments are known as
blocks
.
1
Given that file systems make things like directories and files possible, these trade-offs are usually
seen as a small price to pay.
It is also worth noting that there is no single, universal file system. As
Figure 26.3, “Disk Drive with a
Different File System”
, shows, a disk drive may have one of many different file systems written on it.
As you might guess, different file systems tend to be incompatible; that is, an operating system that
supports one file system (or a handful of related file system types) may not support another. This last
statement is not a hard-and-fast rule, however. For example, Red Hat Enterprise Linux supports a
wide variety of file systems (including many commonly used by other operating systems), making data
interchange between different file systems easy.
Figure 26.3. Disk Drive with a Different File System
Of course, writing a file system to disk is only the beginning. The goal of this process is to actually
store
and
retrieve
data. Let us take a look at our drive after some files have been written to it.
Figure 26.4. Disk Drive with Data Written to It
As
Figure 26.4, “Disk Drive with Data Written to It”
, shows, some of the previously-empty blocks are
now holding data. However, by just looking at this picture, we cannot determine exactly how many files
reside on this drive. There may only be one file or many, as all files use at least one block and some
files use multiple blocks. Another important point to note is that the used blocks do not have to form
a contiguous region; used and unused blocks may be interspersed. This is known as
fragmentation
.
Fragmentation can play a part when attempting to resize an existing partition.
As with most computer-related technologies, disk drives changed over time after their introduction. In
particular, they got bigger. Not larger in physical size, but bigger in their capacity to store information.
And, this additional capacity drove a fundamental change in the way disk drives were used.