Datacenter staff installed Debain 10.4 and left us with
ssh access to the root account, and a minimal lvm filesystem
setup.

To help document and maintain the configuration, declare
the basic storage volumes.

Assuming ssh access to root@mf4.xiph.org, the config
can be applied with:

  ansible-playbook -i hosts mf4.yaml

In theory it should verify the config, but avoid doing anything
destructive if it finds the system in a state that doesn't match
what's described.

This hasn't actually been tested on a bare system; resizing
the root and swap might need manual intervention.