Disk defragmenter in Linux

[Tony Nelson]

At 2:32 PM +0700 12/23/05, Fajar Priyanto wrote:
>Hi all,
>A today's mail from one of the new comer brings me this question again in my
>mind. Linux disk defragmenter. Does it really not needed?
>
>I've been googling around and find that this matter has been discussed as
>early as 1998. And it seems that the only distro that provides a defragmenter
>program is debian.
>
>There are several way of fixing a heavy defragmented disk in Linux, but the
>easiest way is to copy all of the content of the partition into another
>place, completely erase that partition, and copy back the content.
>
>My own experience shows me just that. My /home partition was almost full with
>only 2% freespace. During that time, my Kmail became very slow such as when
>downloading email or when I moved between mail folders. The harddisk was just
>spinning all the time.
>
>Then I copy all my files and mails from the /home partition and move them all
>to another partition. Then delete them from /home. After that, I copied some
>of the files and mail back to /home in order to keep 20% of /home free. So
>far the performance is ok.
>
>However, still the question remains. If Linux ext3 doesn't need defragmenter,
>and able to defrag itself, what is the process name? And when does it run?
>Can I see it in action? Is there an utility to see on what percentage my
>current defragmentation? I tried fschk but no luck.

The opinion that EXT2 doesn't need defragmenting is based on only a
filesystem-level view of the problem, and doesn't consider data read and
write performance.  EXT2 does make an effort to keep data only a short seek
away ("clustered").  With this clustering, the filesystem operations of
adding, removing, extending, and shortening files are not much affected by
fragmentation.

With EXT3 (journalling), which always writes data to a new place, updates
the filesystem info, and then frees the old data (roughly speaking),
fragmentation is a way of life, and there isn't much to be done about it.
Clustering helps by keeping the seeks relatively short, if there is space
nearby.

When you have only 2% free, it's just about certain that the free space is
a long way away from the rest of the data in a file.  Just deleting to get
20% free would probably have fixed your problem.
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