E4DEFRAG(8) System Manager's Manual E4DEFRAG(8)
NAME
e4defrag - online defragmenter for ext4 file system
SYNOPSIS
e4defrag [ -c ] [ -v ] target ...
DESCRIPTION
e4defrag reduces fragmentation of extent based file. The file targeted
by e4defrag is created on ext4 file system made with "-O extent" option
(see mke2fs(8)). The targeted file gets more contiguous blocks and im-
proves the file access speed.
target is a regular file, a directory, or a device that is mounted as
ext4 file system. If target is a directory, e4defrag reduces fragmen-
tation of all files in it. If target is a device, e4defrag gets the
mount point of it and reduces fragmentation of all files in this mount
point.
OPTIONS
-c Get a current fragmentation count and an ideal fragmentation
count, and calculate fragmentation score based on them. By see-
ing this score, we can determine whether we should execute e4de-
frag to target. When used with -v option, the current fragmen-
tation count and the ideal fragmentation count are printed for
each file.
Also this option outputs the average data size in one extent. If
you see it, you'll find the file has ideal extents or not. Note
that the maximum extent size is 131072KB in ext4 file system (if
block size is 4KB).
If this option is specified, target is never defragmented.
-v Print error messages and the fragmentation count before and af-
ter defrag for each file.
NOTES
e4defrag does not support swap file, files in lost+found directory, and
files allocated in indirect blocks. When target is a device or a mount
point, e4defrag doesn't defragment files in mount point of other de-
vice.
It is safe to run e4defrag on a file while it is actively in use by an-
other application. Since the contents of file blocks are copied using
the page cache, this can result in a performance slowdown to both e4de-
frag and the application due to contention over the system's memory and
disk bandwidth.
If the file system's free space is fragmented, or if there is insuffi-
cient free space available, e4defrag may not be able to improve the
file's fragmentation.
Non-privileged users can execute e4defrag to their own file, but the
score is not printed if -c option is specified. Therefore, it is desir-
able to be executed by root user.
AUTHOR
Written by Akira Fujita <a-fujita@rs.jp.nec.com> and Takashi Sato <t-
sato@yk.jp.nec.com>.
SEE ALSO
mke2fs(8), mount(8).
e4defrag version 2.0 May 2009 E4DEFRAG(8)
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