WANT HELP to choose good device on raspberri pi cluster with dockerswarm and portainer

I managed to cluster raspberry pi with docker swarm, I installed portainer.

Now I have a problem, I want to use hdd for nas container (maybe connect it sometime on windows pc), and an ssd for my portfolio website and a service for eve online (attack structure alert) :wink:

how can I be sure to choose the right disk because Iā€™m lost with the volume concept?

Thank you for your advice :wink: and have a good day.