Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 386 — #412
i
i
i
i
i
i
i
i
not allocated in chunks of 1 or 4 kB, but in portions of the exact size
needed. Another benefit lies in the dynamic allocation of inodes. This
keeps the file system more flexible than traditional file systems, like
Ext2, where the inode density must be specified at file system creation
time.
Better Disk Access Performance For small files, you will often find that
both file data and “stat_data” (inode) information are stored next to
each other. They can be read with a single disk I/O operation, mean-
ing that only one access to disk is required to retrieve all the informa-
tion needed.
Fast Crash Recovery Using a journal to keep track of recent metadata
changes makes a file system check a matter of seconds, even for huge
file systems.
18.2.5 JFS
JFS, the Journaling File System was developed by IBM. The first beta version
of the JFS Linux port reached the Linux community in the summer of 2000.
Version 1.0.0 was released in 2001. JFS is tailored to suit the needs of high
throughput server environments where performance is the ultimate goal.
Being a full 64-bit file system, JFS supports both large files and partitions,
which is another reason for its use in server environments.
A closer look at JFS shows why this file system might prove a good choice
for your Linux server:
Efficient Journaling JFS follows a “metadata-only” approach like Reis-
erFS. Instead of an extensive check, only metadata changes generated
by recent file system activity are checked, which saves a great amount
of time in recovery. Concurrent operations requiring multiple con-
current log entries can be combined into one group commit, greatly
reducing performance loss of the file system through multiple write
operations.
Efficient Directory Organization JFS holds two different directory orga-
nizations. For small directories, it allows the directory’s content to be
stored directly into its inode. For larger directories, it uses B
+
trees,
which greatly facilitate directory management.
386 18.2. Major File Systems in Linux