Don't you write full sd to full emmc,only root-partition?
Hmm, yes I do. I write full SD to emmc. I follow the instruction on the referenced page. Step 5 says:
5. bpi-copy /path_to_your_image/xxx.img.zip
So I so with the image that is provided on the same page... I'm sorry if I'm missing something, but there is clearly no evidence that it has to be customised image with the root partition only.
I see dd above writes to mmcblk1,so the full emmc...partition-layout should be same as sd
Yes, it was also my initial understanding that it overwrites the whole emmc with the whole SD image and preserved its structure (ie. partitions in SD image). But in the preceding step (hope already existing) emmc boot partition /dev/mmcblk1boot0 is written with the BPI-R2-EMMC-boot0-0k.img image. And this boot partition takes some 250MB from 8GB emmc. Therefore 8GB SD image could never fit in the remaining space.