Cassandra upgrade/repair issues in migration

I initially just wanted to point at this as a comment, but my rep is too low. So excuse me if this is not a fully fledged answer. (Anyone feel free to edit or hint in comments)

Looking at the documentation at datastax it appears that data will be evently divided by nodes, depending on the "automagical" tokens. From my understanding it's simple as that a new vnode with new tokens just takes an even portion of each node, like all the other nodes already do. Hell, this is even what the doc says basically word by word:

Rebalancing a cluster is no longer necessary when adding or removing nodes. When a node joins the cluster, it assumes responsibility for an even portion of data from the other nodes in the cluster. If a node fails, the load is spread evenly across other nodes in the cluster.

And to address your question:

To further specify my question for virtual nodes does the cluster re-evaluate tokens for all nodes just because a new host has been added?

Sort of. The new node itself takes some partitions (evenly) from all other nodes. If you remove a node every other node will rebalance its partitions from the other nodes, making up for the lost node.

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.