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Chapter 1. System Description 3
1st ed., 6/30/04 - 312579601
Host Software Component Overview
The HSC performs a variety of functions including:
• assisting the tape management system in device allocation
• processing mount and dismount requests
• delivering library mount/dismount instructions to the LMU via a terminal control
unit
• providing exits at key points
• providing for operator control of the library through a set of operator commands and
utility programs
• determining the LSM location of each library cartridge from the library control data
set (CDS).
• providing a programmatic interface for library control.
Integrity of the control data set can be assured through the following techniques employed
at an installation:
• allocating secondary (shadow) and standby data sets in addition to the primary
control data set
• scheduling regular backups of the control data sets
• utilizing journal data sets to log library transactions.
After processing a mount or dismount request from the tape management system, the HSC
issues cartridge movement requests to an LMU station via the terminal control unit. The
LMU relays information to the Library Control Unit (LCU) enabling the robot in the LSM
to locate and mount/dismount the requested cartridge.
In a dual LMU environment when the master LMU fails, the standby LMU takes over. The
standby LMU completes the work in progress and services all future ACS requests.