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Storage Architectures and Devices 105
4.2.6 Summary of SCSI Specifications
SCSI defines many different modes of operation, including several different
data transfer modes. The most common are shown in Table 19.
Table 19. Differential SCSI Modes
4.3 SCSI Cabling
It is very likely that you will face problems regarding configuration and
installation of SCSI adapters and devices.
SCSI cabling can be one of the most confusing topics to encounter. Some of
the questions that may arise are:
• How many SCSI devices can be attached to a single SCSI adapter?
• What are the right cable features to attach more SCSI devices on the
same SCSI chain?
• What is the right SCSI cabling for an HACMP configuration?
In this section, the main SCSI cabling features used with PCI-based RS/6000
systems are described, answering some of the questions mentioned above.
Mode Bandwidth Frequency Max. data
Transfer
Rate
Max. Cable
Length
Single Ended
SCSI-I 8-bit 5 MHz 5 MB/s 6 meters
Fast SCSI 8-bit 10 MHz 10 MB/s 3 meters
Fast/Wide SCSI 16-bit 10 MHz 20 MB/s 3 meters
Ultra SCSI (or
Fast-20 SCSI)
8-bit 20 MHz 20 MB/s 1.5 meters
Wide Ultra (or
FAST-20 Wide
SCSI)
16-bit 20 MHz 40 MB/s 1.5 meters
Ultra2 SCSI 16-bit 40 MHz 80 MB/s 12 meters
The single-ended length refers to the length of the SCSI cable without
using devices and their main characteristics.
Note