Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 382 — #408
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18.1 Glossary
metadata A file system–internal data structure that assures all the data on
disk is properly organized and accessible. Essentially, it is “data about
the data.” Almost every file system has its own structure of metadata,
which is partly why the file systems show different performance char-
acteristics. It is of major importance to maintain metadata intact, be-
cause otherwise all data on the file system could become inaccessible.
inode Inodes contain various information about a file, including size,
number of links, date and time of creation, modification, and access,
and pointers to the disk blocks where the file contents are actually
stored.
journal In the context of a file system, a journal is an on-disk structure
containing a kind of log in which the file system stores what it is
about to change in the file system’s metadata. Journaling greatly re-
duces the recovery time of a Linux system because it obsoletes the
lengthy search process that checks the entire file system at system
start-up. Instead, only the journal is replayed.
18.2 Major File Systems in Linux
Unlike two or three years ago, choosing a file system for a Linux system is
no longer a matter of a few seconds (Ext2 or ReiserFS?). Kernels starting
from 2.4 offer a variety of file systems from which to choose. The following
is an overview of how these file systems basically work and which advan-
tages they offer.
It is very important to bear in mind that there may be no file system that
best suits all kinds of applications. Each file system has its particular
strengths and weaknesses, which must be taken into account. Even the
most sophisticated file system cannot substitute for a reasonable backup
strategy, however.
The terms data integrity and data consistency, when used in this chapter, do
not refer to the consistency of the user space data (the data your application
writes to its files). Whether this data is consistent must be controlled by the
application itself.
382 18.1. Glossary