termination and covers radial configurations with the DWZZH UltraSCSI hubs and
This chapter discusses the following topics:
•Shared SCSI bus configuration requirements (Section 3.1)
•SCSI bus performance (Section 3.2)
•SCSI bus device identification numbers (Section 3.3)
•SCSI bus length (Section 3.4)
•SCSI bus termination (Section 3.5)
•UltraSCSI hubs (Section 3.6)
•Configuring UltraSCSI hubs with RAID array controllers (Section 3.7)
3.1Shared 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
•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
•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 9.2 for more information.
•Be careful when performing maintenance on any device that is on a shared bus because of the constant activity on the bus. Usually, to perform maintenance on a device without shutting down the cluster, you must be able to isolate the device from the shared bus without affecting bus termination.
