Compaq AA-RHGWC-TE manual Scsi Bus Performance, Scsi Bus Versus Scsi Bus Segments

storage arrays (HSZ70 and HSZ80), or RA8000 or ESA12000 storage arrays (HSZ80 and HSG80). Older, non-UltraSCSI BA356 shelves are supported with UltraSCSI host adapters and host RAID controllers as long as they contain no UltraSCSI disks.

•UltraSCSI drives and fast wide drives can be mixed together in an UltraSCSI BA356 shelf (see Chapter 9).

•Differential UltraSCSI adapters may be connected to either (or both) a non-UltraSCSI BA356 shelf (via a DWZZB-VW) and the UltraSCSI BA356 shelf (via the DS-BA35X-DA personality module) on the same shared SCSI bus. The UltraSCSI adapter negotiates maximum transfer speeds with each SCSI device (see Chapter 9).

•The HSZ70 and HSZ80 UltraSCSI RAID controllers have a wide differential UltraSCSI host bus with a Very High Density Cable Interconnect (VHDCI) connector. HSZ70 and HSZ80 controllers will work with fast and wide differential SCSI adapters (for example, KZPSA-BB) at fast SCSI speeds.

•Fast, wide SCSI drives (green StorageWorks building blocks (SBBs) with part numbers ending in -VW) may be used in an UltraSCSI BA356 shelf.

•Do not use fast, narrow SCSI drives (green SBBs with part numbers ending in -VA) in any shelf that could assign the drive a SCSI ID greater than 7. It will not work.

•The UltraSCSI BA356 requires a 180-watt power supply (BA35X-HH). It will not function properly with the older, lower-wattage BA35X-HF universal 150-watt power supply (see Chapter 9).

•An older BA356 that has been retrofitted with a BA35X-HH 180-watt power supply and DS-BA35X-DA personality module is still only FCC certified for Fast 10 configurations (see Chapter 9).

3.2SCSI Bus Performance

Before you set up a SCSI bus, it is important that you understand a number of issues that affect the viability of a bus and how the devices connected to it operate. Specifically, bus performance is influenced by the following factors:

•Transmission method (Section 3.2.2)

•Data path (Section 3.2.3)

•Bus speed (Section 3.2.4)

3.2.1SCSI Bus Versus SCSI Bus Segments

An UltraSCSI bus may comprise multiple UltraSCSI bus segments. Each UltraSCSI bus segment comprises electrical conductors that may be in a

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