Compaq AA-RHGWC-TE manual Shared Scsi Bus Configuration Requirements

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 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 9.1 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 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.

•All supported UltraSCSI host adapters support UltraSCSI disks at UltraSCSI speeds in UltraSCSI BA356 shelves, RA7000 or ESA10000

3–2Shared SCSI Bus Requirements and Configurations Using UltraSCSI Hardware