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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
improves 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
e4defrag to target. When used with -v option, the current frag‐
mentation 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
after 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
device.

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)

Si Windows n'arrive pas à lire le disque c'est qu'il y a plus grave qu'un problème de fragmentation à mon avis.
Par ailleurs, si ce disque est lisible, Linux devrait être capable de l'ouvrir.

JLB

Et en montant ce disque sur une machine virtuelle (même si l'opération sera probablement plus longue) ?

Sinon, depuis ta distribution préférée Linux, monter le disque pour récupérer les données afin de les copier ailleurs (sous réserve de la masse de données) et pouvoir ensuite reformater ce disque ? ... Méthode un peu bourrin mais ....