NonStop S-Series Server Description Manual (G06.24+)

Input/Output Operations
HP NonStop S-Series Server Description Manual—520331-003
10-4
Overview of the I/O System
Overview of the I/O System
Figure 10-2 expands upon information presented in Section 1, Introduction (see
Figure 1-8 on page 1-15). In this figure, those components that make up the ServerNet
hardware are highlighted in the central part of the illustration. These details are mostly
eliminated in succeeding illustrations for the sake of simplicity.
Starting at the top, note that the processor typically has several layers of I/O software;
the actual components in these layers differs between storage I/O and communications
I/O, as explained in the previous topic. In either case, however, both kinds of I/O
interface to the ServerNet hardware through a collection of procedures called
ServerNet services. The ServerNet services provide the hardware-accessible tables,
buffers, and descriptors that the processor ServerNet interface can use for transferring
ServerNet packets through the ServerNet links. The primary components of the
processor ServerNet interface are the bus transfer engine (BTE) and the access
validation and translation (AVT) logic.
ServerNet routers (two of which are shown, marked X and Y) provide massive
expandability of the ServerNet links, as detailed in Section 1, Introduction. On the
multifunction I/O boards (MFIOBs) within either a processor enclosure or an I/O
enclosure, these routers provide ServerNet links to a ServerNet bus interface (SBI) on
the same MFIOB, and two ServerNet adapters. The ServerNet adapters, unlike the
MFIOBs, connect to both X and Y fabrics. The unused router ports in the figure are
available for ServerNet expansion.
The ServerNet bus interfaces provide conversion of ServerNet protocol to whatever
protocol is used by the buses associated with the various controllers. Depending on
the kind of bus that is used, a secondary converter may be required such as in the
case of the SCSI protocol. A single SBI can, depending on design, provide bus
conversion for several controllers—four in the case of the MFIOB.
Each controller has its own ServerNet ID, as explained in Section 2, Principles of
System Operation (see Figure 2-2 on page 2-5), and is therefore fully described as a
ServerNet addressable controller (SAC). Each controller has its own RISC processor
and local memory, from which it runs its own native code and specially modified code
for ServerNet usage.
There are three SCSI controllers on the MFIOB. Two of these controllers are matched
in pairs with the two MFIOBs in an enclosure, so that each SCSI bus can be controlled
through either the X fabric or the Y fabric. These two buses are typically used for
multiple disk drives. The third SCSI port, a differential SCSI port, is typically used for a
tape drive.
The communications controller on the MFIOB provides a port for the serial
maintenance bus (SMB) and an Ethernet port.