From Rackspace OnMetal: The Right Way To Scale:
OnMetal servers are single-tenant, bare-metal servers provisioned via the same OpenStack API as our cloud. They can be spun up as quickly as VMs to offer the agility of multi-tenant environments with the performance of single-tenant hardware.
Going from an EC2 style “spin up a VM via API call” to a “spin up a whole server via API call” seems like the next logical step. There are more challenges when it comes to managing this at a whole server level instead of VMs, but with new challenges come new opportunities.
One important note, there is reportedly no VM layer on these servers. It isn’t just a single-tenant VM, but an actual bare-metal server.