L700 (CTL700) Installation and User's Guide (G06.24+, H06.03+)

Managing Tape Drives
L700 (CTL700) Installation and User’s Guide—527338-004
9-13
Controlling Data Compression
Using MEDIACOM to Set the Systemwide Compression
Default
MEDIACOM is the operator interface to the Distributed Systems Management
(DSM)/Tape Catalog.
The compression attribute of the ALTER MEDIADEFS command has two
possible settings: COMPRESSION IDRC and COMPRESSION OFF. The
default setting is COMPRESSION OFF. When COMPRESSION IDRC is
specified, compression mode is turned on for the 9840 tape drive.
To check and set the systemwide compression default specification:
1. Enter MEDIACOM at the TACL prompt:
-> MEDIACOM
MEDIACOM-T6028D42 (18DEC98)
MC>
2. Display the current system setting for compression:
MC> INFO MEDIADEFS
Support Level NOCATALOG
Automatic OFF
Compression OFF
MC>
Compression OFF means that by default, compression is not attempted
during a write to a scratch tape volume.
Table 9-1. Methods for Controlling Data Compression
Method Description
MEDIACOM The MEDIACOM ALTER MEDIADEFS command sets a
systemwide default.
The CLASS
TAPECATALOG
DEFINE command
The CLASS TAPECATALOG DEFINE can specify the
compression default for one job. (It overrides the current
systemwide default.)
The SETMODE 162
procedure call
The SETMODE 162 procedure call can specify the
compression mode for one write command. (It overrides
the current system wide default.)
Note. Only super-group users (user ID 255,n) can issue the ALTER MEDIADEFS command.