e4defrag

E4DEFRAG(8)                 System Manager's Manual                E4DEFRAG(8)

NAME
       e4defrag - online defragmenter for ext4 filesystem

SYNOPSIS
       e4defrag [ -c ] [ -v ] target ...

DESCRIPTION
       e4defrag  reduces fragmentation of extent based file. The file targeted
       by e4defrag is created on ext4 filesystem 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 filesystem.  If target is a directory, e4defrag reduces fragmenta-
       tion 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 filesystem  (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)