Physical Configuration; System Expansion - Compaq SW TL881 DLT Mini-Lib/1 Manual

1-6 Compaq TL881 Minilibrary System Users Guide

Physical Configuration

System Expansion

Drives
With a standard SCSI interface, modules equipped with DLT 20/40 drives
have a native data transfer rate of 1.5 MB/second, 3.0 MB/sec for two drives.
The rates for compressed data are dependent on compression ratio, record size,
data type, and other system parameters, but averages approximately 1:7.
Internal Cabling Configuration
The differential version of the MiniLibrary base module is wired in an
independent-bus SCSI configuration. That is, the robotics and each of the
drives has its own SCSI bus. SCSI jumpers are available for those applications
requiring that some combination of drives and robotics be daisy-chained to a
single SCSI bus. The single-ended table-top version, however, has the first
driver daisy-chained internally to the robotics in order to reduce cable length.
These configurations are described in more detail in the section on SCSI
Interfaces in Chapter 3, Installation.
The Expansion Unit must be mounted at the top of the stack, which places its
control panel at a convenient height. The control panels of the MiniLibrary
Base Modules and Data Units are of secondary importance, as they serve
mainly to help localize system failures. When installed, the motor drive
assembly of the Pass-Thru Mechanism is directly behind the Expansion Unit.
MiniLibrary Base Modules may be installed anywhere below the Expansion
Unit, in any order. There may be a slight performance advantage in making the
MiniLibrary Base Modules contiguous, but gaps are permitted. The size of a
gap is limited by the fact that each gap must be bridged by some number of 7"
Pass-Thru Mechanism track sections. For safety, available cover plates should
be installed on all Pass-Thru Mechanism sections that are not connected to
MiniLibrary modules.
The Expansion Unit senses the position of each module during initialization at
power-up. Even if there are gaps between modules, the system will operate
correctly. If you plan to leave gaps between modules, be sure to order
additional Pass-Thru Mechanism track segments and cover plates equal to the
length of the gap.
A MiniLibrary system may be expanded in capacity and performance by
adding or removing TL881 modules. Associated with the Expansion Unit and
each MiniLibrary Base Module is a section of the Pass-Thru Mechanism.