Hello @ega,
This is an advanced use case and it is not covered by Yunohost itself. The goal is to be easy and straightforward for most people and rely on the backup/restore system instead of hard drive redundancy.
So you should install a base debian and then install yunohost on top of it. Yunohost does not mind on what is installed.
@JimboJoe has an installation with raid + luks here Yunohost + RAID? (in french but you should get the idea 
)