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Table 3–2: SCSI Bus Segment Length
SCSI Bus Bus Speed Maximum Cable Length
Narrow, single-ended 5 MB/sec
6 meters
Narrow, single-ended fast 10 MB/sec
3 meters
Wide differential, fast 20 MB/sec
25 meters
Differential UltraSCSI 40 MB/sec
25 meters
a
a
The maximum separation between a host and the storage in a TruCluster Server configuration is 50
meters: 25 meters between any host and the UltraSCSI hub and 25 meters between the UltraSCSI hub
and the RAID array controller.
Because of the cable length limit, you must plan your hardware configuration
carefully, and ensure that each SCSI bus meets the cable limit guidelines.
In general, you must place systems and storage shelves as close together as
possible and choose the shortest possible cables for the shared bus.
3.5 Terminating the Shared SCSI Bus when Using UltraSCSI
Hubs
You must properly connect devices to a shared SCSI bus. In addition, you
can terminate only the beginning and end of each bus segment (either
single-ended or differential).
There are two rules for SCSI bus termination:
• There are only two terminators for each SCSI bus segment. If you use an
UltraSCSI hub, you only have to install one terminator.
• If you do not use an UltraSCSI hub, bus termination must be external.
External termination is covered in Section 9.2.
______________________ Notes ______________________
With the exception of the TZ885, TZ887, TL890, TL891, and
TL892, tape devices can only be installed at the end of a shared
SCSI bus. These tape devices are the only supported tape devices
that can be terminated externally.
We recommend that tape loaders be on a separate, shared SCSI
bus to allow normal shared SCSI bus termination for those shared
SCSI buses without tape loaders.
Whenever possible, connect devices to a shared bus so that they can be
isolated from the bus. This allows you to disconnect devices from the bus
for maintenance purposes, without affecting bus termination and cluster
operation. You also can set up a shared SCSI bus so that you can connect
additional devices at a later time without affecting bus termination.
Shared SCSI Bus Requirements and Configurations Using UltraSCSI Hardware 3–7