You will not be able to create a VDO device on top of a disk smaller than 5GB. See screenshots from my lab:
- 4GB-error.png (42.69 KiB) Viewed 14508 times
- 5GB-OK.png (11.31 KiB) Viewed 14508 times
This looks to be a limitation from RedHat, although I was not able to find anything like that in their VDO documentation.