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This is especially critical if you will install tape devices on the shared
SCSI bus. 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.
• Place the devices as close together as possible and ensure that shared
SCSI buses will be within length limitations.
• Prepare the systems and storage shelves for the appropriate bus
connection, including installing SCSI controllers, UltraSCSI hubs,
trilink connectors, and SCSI signal converters.
After you install all necessary cluster hardware and connect the shared
SCSI buses, be sure that the systems can recognize and access all the shared
disks (see Section 4.3.2). You can then install the TruCluster Server software
as described in the TruCluster Server
Software Installation manual.
4.1 Planning Your TruCluster Server Hardware
Configuration
Before you set up a TruCluster Server hardware configuration, you must
plan a configuration to meet your performance and availability needs. You
must determine the following components for your configuration:
• Number and type of member systems and the number of shared SCSI
buses
You can use two to eight member systems for TruCluster Server. A
greater number of member systems connected to shared SCSI buses
gives you better application performance and more availability. However,
all the systems compete for the same buses to service I/O requests, so a
greater number of systems decreases I/O performance.
Each member system must have a supported SCSI adapter for each
shared SCSI bus connection. There must be enough PCI slots for the
Memory Channel cluster interconnect(s) and SCSI adapters. The number
of available PCI slots depends on the type of AlphaServer system.
• Cluster interconnects
You need only one cluster interconnect in a cluster. For TruCluster
Server Version 5.1, the cluster interconnect is the Memory Channel.
However, you can use redundant cluster interconnects to protect against
an interconnect failure and for easier hardware maintenance. If you
have more than two member systems, you must have one Memory
Channel hub for each interconnect.
4–2 TruCluster Server System Configuration Using UltraSCSI Hardware