Rack Components

The Service Processor (SP) allows for control and operation of various components of the rack over the management network. The SP is always used in conjunction with a Root of Trust (RoT).

There are three types of boards that contain an SP: the server sled (Cosmo or Gimlet), the rack switch (Sidecar), and the power shelf controllers (PSC). Each SP runs a software image built specifically for that board type.

Each server sled includes both a host CPU and SP. While the host CPU operates customer (and control plane) workloads, the service processor is responsible for certain chassis management functions (e.g., thermal control) and provides essential interfaces to the control plane for functions like host system power control, access to the system’s serial console, and upgrade of some device software.

Each rack contains two switches, known as “Sidecars”. Each Sidecar contains a Tofino switch ASIC that’s responsible for switching both control plane traffic and data plane (user) traffic within the rack and routing traffic outside the rack. Every sled in the rack has one physical network connection to each of the two Tofino switches (via the rack backplane).

Each Sidecar includes an SP — just like server sleds — but there is no host system within a Sidecar. Rather, the Tofino switch is connected via an external PCIe cable to one of the adjacent server sleds. The sidecar-adjacent sleds (a.k.a. "Scrimlets") have the unique ability to control, monitor, and exchange network traffic with the Tofino switch.

Each Sidecar also has a separate management network switch used exclusively for providing connectivity to the different SPs in the rack.

Each rack typically comes with two power shelves. A power shelf is largely a passive backplane that houses six rectifiers and a Power Shelf Controller (PSC). Without a PSC, the power shelf remains largely functional, handling loss and restoration of external power as well as failures of individual rectifiers. The PSC gives us:

The PSC, while a much simpler system than sled or sidecar, also contains an SP. The PSC’s SP has dedicated pins for presence and on/off control for each rectifier. It differs from the SP in a sled or sidecar in that it is the main component of the PSC whereas those other SPs control the main component.

The latest product specifications are available at oxidecomputer.com.