HP NonStop G-Series - Manual (Page 82)

Configuring DSM/TC
DSM/Tape Catalog User’s Guide — 520233-008
5 - 8
Default Retention
Three retention mechanisms are supported:
Retention Period Specified for BACKUP
The retention period for a disk file specified in a TAPECATALOG DEFINE is used for
the BACKUP operation. Because each instance of BACKUP creates one tape file,
there is only one retention period for all the disk files in an entire backup. Therefore, all
disk files created by a single invocation of BACKUP expire simultaneously. The
retention period specified for BACKUP applies to both the BACKUP utility (T9074) and
Backup and Restore 2.0 BACKUP.
The Expiration Process
The retention period is stored with each tape file record in the file catalog. A tape
volume becomes scratch when all the tape files on the volume set expire. DSM/TC
monitors the system date and automatically recognizes when tape files are due to
expire. DSM/TC locates all tape files that are due to expire, marks them as expired,
and determines if the tape volumes containing them should become scratch tape
volumes. $ZSVR initiates this expiration process daily.
Monitoring the System Date
Because tape file retention is based on the system date, an incorrectly entered system
date can be problematic. If the operator sets the system date too far in the future,
existing tape files could be deleted prematurely. To avoid this, DSM/TC performs a
reasonability check on the system date. DSM/TC remembers when it last tried to
perform tape file expiration. Each time the expiration process is started, DSM/TC
checks the current date against the date when it last executed. If the date changes by
more than three days, the operator must confirm that the system date is entered
properly.
Time-based
retention Time-based retention instructs the file catalog to retain the file generation until
a specified period of time has passed. Time-based retention is specified in
number of days. The default retention value is 30 days.
Date-based
retention Date-based retention instructs the file catalog to retain the tape file until a
specified date.
Permanent
retention Permanent retention instructs the file catalog to retain the tape file indefinitely.
Generations and retentions are based on the tape file. When a new tape file
record is created, you can specify a retention period in the TAPECATALOG
DEFINE for the tape file. If no retention period is explicitly specified, the
DSM/TC default retention period as specified through the MEDIACOM ALTER
MEDIADEFS command is used. The default retention can be time based or
permanent. It cannot be date based. Explicitly specifying a retention period in
the TAPECATALOG DEFINE overrides the default retention period specified
through ALTER MEDIADEFS.