5190/5194 Modular Tape Subsystem Manual

Operating the Cartridge Tape Drive and ACL
5190/5194 Modular Tape Subsystem Manual—426878-002
4-50
Using a DEFINE to Override the Systemwide
Compression Default Setting
For more information about MEDIACOM and the ALTER MEDIADEFS command, see
the DSM/Tape Catalog Operator Interface (MEDIACOM) Manual.
Using a DEFINE to Override the Systemwide Compression
Default Setting
The systemwide compression default setting set by the MEDIACOM ALTER
MEDIADEFS command applies to labeled and unlabeled tapes. After you set the
systemwide default setting, the drives on the system always write using the default
setting. You can override the default setting for a specific job by using a CLASS
TAPECATALOG DEFINE.
A CLASS TAPECATALOG DEFINE is a named set of attributes and values that specify
information about a tape file. If you use labeled tape, you must create a CLASS
TAPECATALOG DEFINE for each tape file to be accessed on that tape before you can
use the tape.
Using a CLASS TAPECATALOG DEFINE
There are two types of tape DEFINEs:
•
CLASS TAPE DEFINEs
•
CLASS TAPECATALOG DEFINEs
If you are using the DSM/TC system, you must use a CLASS TAPECATALOG
DEFINE. A CLASS TAPECATALOG DEFINE is similar to a CLASS TAPE DEFINE, but
the CLASS TAPECATALOG DEFINE has two additional attributes:
CATALOG { ON | OFF }
Requests the services of the DSM/TC system (which might not be installed on your
system). Specify OFF to use the CLASS TAPECATALOG DEFINE template
without using DSM/TC. Specify ON to use DSM/TC.
COMPRESSION { IDRC | OFF }
Overrides the systemwide default compression setting on a job-by-job basis for
any tape in a 5190 drive. (The 5194 tape drive is unaffected by this attribute.)
COMPRESSION can be set on (IDRC) or OFF.
Considerations
•
After executing an I/O operation using a CLASS TAPECATALOG DEFINE, the
system returns to the systemwide compression default setting for the next job.
•
If you don’t specify the COMPRESSION attribute in the DEFINE, the system uses
the systemwide default compression setting set by the MEDIACOM ALTER
MEDIADEFS command.