I wonder if this is at all related to a case I've seen where VM images
aren't being compressed at all. 'nodatacow' is not set. Does not
matter if compress or compress-force is set. And if I merely copy the
file, --reflink=never, the result is fairly well compressed.

VM is qemu-kvm based. And I've tried either cache none or writeback
(maybe both, I forget) and cache unsafe. No compression.

*shrug*

--
Chris Murphy