jamesd2: The problem is, Oracle doesn't like you doing that. They say they'll accept Containerization of the database for the purposes of determining CPU/core count, but then they say "oh! Not running in the global Zone! UNSUPPORTED!"
They're being greedy, just like they always have.
Otherwise, yeah, it'd make perfect sense to dedicate a few cores to the OS so ZFS could stay well fed, and shave that off the DB cost of the box.