Well, After a long time with this probleme I can say it could be because my disk is an xfs drive, according to this there is a problem since 2005 !!!
http://bugzilla.gnome.org/show_bug.cgi?id=363400 ** Summary changed: - Slow file transfert with mounted disks (fat32 or ntfs-3g etc..) + Slow file transfert with mounted disks (XFS fat32 or ntfs-3g etc..) ** Tags added: xfs -- Slow file transfert with mounted disks (XFS fat32 or ntfs-3g etc..) https://launchpad.net/bugs/70097 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs