4.1 The Addressing Limitations of HP-UX

As discussed in the previous chapter, Fibre Channel allows a potentially very large number of available addresses. However, this large number of available addresses does not fit seamlessly into the current addressing model in the HP-UX operating system. To handle the number of possible addresses, the Fibre Channel Protocol (FCP) subsystem on HP-UX uses three methods of addressing:

• Peripheral Device addressing

• Logical Unit addressing

• Volume Set addressing

But first, there are two major limitations and work-arounds that need to be explained.

4.1.1 Target Address Space Limitations

Figure 4-1. Target Address Space Limitations

Parallel SCSI has the capacity to handle 16 IDs (targets or devices) per bus, 15 devices and one controller. The controller is the HBA. FC-AL, however, has a much larger potential number of targets that can be addressed, 0 “125 or 126 devices.

4.1.2 LUN Address Space Limitations

Figure 4-2. LUN Address Space Limitations

Parallel SCSI has the capacity to handle eight LUNs per target or device. FC-AL, however has a huge potential number of LUNs: 2 ⁶⁴ .

4.1.3 Work-arounds for Target Address Space Limitations

In order to address the 126 targets allowed by FC-AL, HP-UX incoporates the use of virtual busses . Each virtual bus addresses a group of 16 FC-AL targets.

Figure 4-3. Work-around for Target Address Limitations

4.1.4 Work-around for LUN Address Space Limitations

In order to address all the allowable LUNs, HP-UX enables 128 LUNs per virtual bus.

Figure 4-4. Work-around for LUN Address Limitations