NonStop S-Series Server Description Manual (G06.27+)

Introduction

HP NonStop S-Series Server Description Manual—520331-004

1-20

Components of I/O Multifunction (IOMF) CRU

The I/O multifunction (IOMF) CRU is the component that determines that a system

enclosure is an I/O enclosure rather than a processor enclosure. (Refer back to

Figure 1-3 on page 1-7.)

IOMF CRUs are installed in pairs in an I/O enclosure. The IOMF in slot 50 of the

enclosure is for the X fabric, and the IOMF in slot 55 is for the Y fabric. This pairing

provides fault tolerance for I/O operations to devices connected to the enclosure.

The IOMF CRU consists of two boards and a power supply. The two boards are the

multifunction I/O board (which is identical to that shown earlier for the PMF CRU; see

Figure 1-4 on page 1-9) and the ServerNet buffer board (SBB).

An approximate representation of the IOMF CRU is shown in Figure 1-11.

As mentioned in Components of Processor Multifunction (PMF) CRU on page 1-8, the

MFIOB has six main logic elements: the ServerNet router, the ServerNet bus interface,

and four ServerNet addressable controllers.

The ServerNet buffer board contains logic for sending and receiving ServerNet packets

to and from other enclosures. It provides the necessary ServerNet cable connectors.

There are two versions of the IOMF CRU. The original version, simply designated as

IOMF, uses six-port routers, and the later version (IOMF 2) uses 12-port routers. Only

7 of the 12 router ports are assigned in the case of IOMF 2. The additional port

provided by the IOMF 2 permits segregating disk operations from those operations that

occur through the ethernet and differential SCSI ports. (See Figure 1-7 and Figure 1-8

on page 1-15 for a comparison of these two configurations.) The result of this

segregation is higher overall I/O throughput for all external I/O operations that occur

through this board. For convenience, most documents for NonStop servers, including

this manual, generally omit the 2 designator in IOMF 2 and simply use IOMF as a

generic term.