Telling what needs to be done and how exactly to do it are two different things. I can only say what is needed, as in my previous post. You should know your platform and the infrastructure to translate it to your needs. Pl. keep in mind: this is free advice in a public forum. I do not take responsibility for any mishaps.
That said, you can reduce the risk to a minimum by _copying_ the moodledata to the new disk (as opposed to _moving_). If the new disk gives problems, you can always fall back to the old disk. "Don't burn the bridges!"
If you ask me, if the Moodle server is valuable to your institution and it has the resources, I would design a new server, do a test migration first, test thoroughly including the performance. See https://moodle.org/mod/forum/discuss.php?d=418615#p1689018
Once everything is fine, do the real transition. Even then I would keep the old server "cold" until the transition has been tested by everybody and has been accepted.