Setup Cassandra Database
Q2: If I understand your question correctly, I don't think you want to do that nor should you use Cassandra if that's what you're trying to do. Cassandra is meant to spread data across nodes so that if one node fails then you don't lose your data or crash the entire cluster. If you are putting only specific data one one single hard drive, than you're compromising how Cassandra works. 

What's your use case for Cassandra? Why don't you transfer the SSD drive data to a commodity disk then just unplug the SSD and use it for something else? Why do you need Cassandra specifically? Do you have an insane number of writes? What size data are you working with? If you're read heavy you might be better off with a different database.