First reduce the size of the filesystem on the logical volume. For
ext2/ext3 filesystems, you can use resize2fs for this. I usually make
the filesystem size smaller than the size I eventually want it to be (to
allow a safety margin), then run resize2fs again (or ext2online) after
shrinking the logical volume to get the filesystem using the full size
of the volume.
Ok, thanks. I've never heard about this resize2fs tool. That was, what I was missing.
boris