The steps for specifying a disk for deployment must be added to the RHOSP 9 Bare Metal Provisioning guide. This includes mentioning that a suitable disk device can be found by using its name or path (or by other identifiers). See http://docs.openstack.org/project-install-guide/baremetal/draft/advanced.html#specifying-the-disk-for-deployment-root-device-hints for an upstream example.
Assigning to Sandra for review.
Content has been published: https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/9/html/bare_metal_provisioning/