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Managing Tape Drives
L700 (CTL700) Installation and User’s Guide—527338-004
9-15
Controlling Data Compression
COMPRESSION { ON | OFF }
Overrides the systemwide default compression specification on a
job-by-job basis for any tape in the tape drive. Compression can be set
ON or OFF.
Examples
All examples assume that DSM/TC will not be used. Examples 1 and 2 show
CLASS TAPECATALOG DEFINES specified for BACKUP operations.
Example 1
This example for a labeled tape specifies a CLASS TAPECATALOG DEFINE
named =BACK with compression on (IDRC). The USE OUT attribute specifies
to write the file to tape. The BACKUP command copies all the files in the $DATA
volume to tape. The LISTALL option lists the names of all files backed up, and
the NOUNLOAD option directs BACKUP to rewind the final tape and leave it
online when the BACKUP operation is completed.
->ADD DEFINE =BACK, CLASS TAPECATALOG, LABELS BACKUP,
& CATALOG OFF, COMPRESSION IDRC, USE OUT
->BACKUP =BACK, $DATA.*.*, LISTALL, NOUNLOAD
Example 2
This example for an unlabeled tape specifies a CLASS TAPECATALOG DEFINE
named =UNLABEL with compression off. For unlabeled tape, a device must be
specified in the DEFINE (in this example, DEVICE $TAPE1). Because it is an
unlabeled tape, the LABELS attribute has the value OMMITED.
->ADD DEFINE =UNLABEL, CLASS TAPECATALOG, & LABELS
OMMITTED, CATALOG OFF, DEVICE $TAPE1, & COMPRESSION OFF
->BACKUP =UNLABEL, $DATA.*.*, LISTALL, NOUNLOAD
Notes.
•
After executing a CLASS TAPECATALOG DEFINE, the system returns to the systemwide
default specification for the next job.
•
If the COMPRESSION attribute is not specified in the DEFINE, the system uses the
default compression specification set by the MEDIACOM ALTER MEDIADEFS command.
•
If no default specification was set using the ALTER MEDIADEFS command, the default
compression specification for any tape on the tape drive is OFF.
•
Applications specifying a CLASS TAPE DEFINE always use the systemwide default
specification for compression because there is no COMPRESSION attribute for a CLASS
TAPE DEFINE.