i've problems with this. If i try store uncompressed the metadata of the second SD card partition (/dev/sdb2 = rootfs) the generated image file is nearly big as the whole partition. In compressed state it's 25 MB. Is this expected?
Also can get filesystem metadata image of your card like:
e2image -r <fs-device> - | gzip >/tmp/ext4-image.gz
and put it somewhere for download? The image will contain only fs metadata,
not data so it should be relatively small and we won't have access to your
secrets ;). With the image we'd be able to see how the free space looks
like and whether it perhaps does not trigger some pathological behavior.