Technical data

______________________ Note _______________________
Although the UltraSCSI BA356 might have been included
in this chapter with the other UltraSCSI devices, it is not.
The UltraSCSI BA356 is discussed in Chapter 10 with the
configurations using external termination. It cannot be cabled
directly to an UltraSCSI hub because it does not provide SCSI
bus termination power (
termpwr).
In addition to using only supported hardware, adhering to the requirements
described in this chapter will ensure that your cluster operates correctly.
Chapter 10 contains additional information about using SCSI bus signal
converters, and also contains diagrams of TruCluster Server configurations
using UltraSCSI and non-UltraSCSI storage shelves and RAID array
controllers. The chapter also covers the older method of using external
termination and covers radial configurations with the DWZZH UltraSCSI
hubs and non-UltraSCSI RAID array controllers.
3.1 Shared SCSI Bus Configuration Requirements
A shared SCSI bus must adhere to the following requirements:
• Only an external bus can be used for a shared SCSI bus.
• SCSI bus specifications set a limit of 8 devices on an 8-bit (narrow) SCSI
bus. The limit is 16 devices on a 16-bit SCSI bus (wide). See Section 3.3
for more information.
• The length of each physical bus is strictly limited. See Section 3.4 for
more information.
• You can directly connect devices only if they have the same transmission
mode (differential or single-ended) and data path (narrow or wide). Use
a SCSI signal converter to connect devices with different transmission
modes. See Section 10.1 for information about the DWZZA (BA350) or
DWZZB (BA356) signal converters or the DS-BA35X-DA personality
module (which acts as a differential to single-ended signal converter
for the UltraSCSI BA356).
• For each SCSI bus segment, you can have only two terminators, one
at each end. A physical SCSI bus may be composed of multiple SCSI
bus segments.
• If you do not use an UltraSCSI hub, you must use trilink connectors and
Y cables to connect devices to a shared bus, so you can disconnect the
devices without affecting bus termination. See Section 10.2 for more
information.
3–2 Shared SCSI Bus Requirements and Configurations Using UltraSCSI Hardware