HP Archive Backup System for OpenVMS Guide to Operations

3.4.3 Compression
3.4.4 Data Safety
3.4.5 Drive Count
Saving and Restoring Data
3.4 Environments
• RECORD_DATE - Modify the BACKUP date to reflect the time that this file was backed
up; this is the required option if you intend to do incremental backups of this file, and is the
default value - supported for files of type VMS_FILES only.
• NO_CHANGE - Do not change the online file at all. If this option is specified, you will not
be able to perform incremental saves on this file.
• DELETE_FILE - This option is used when the backup is intended to be a long-term archive
and you wish the file to be removed from the online system. The file is only deleted on a
successful save operation.
Although RECORD_DATE is supported for VMS_FILES only, it remains the default for all data
types, and is simply ignored for the other types.
ABS supports the following types of compression for UNIX clients:
• No compression (default)
• UNIX Compression
• GZIP Compression
It is recommended that you either use the default UNIX environment (UNIX_BACKUPS_ENV)
or a single user-created environment for all your UNIX client saves, using a single type of compression
for all UNIX saves. If you mix compression types among your UNIX saves, you should
be very careful to assign the appropriate environment on any restore. If you specify the wrong
compression option on a restore, then ABS will not be able to restore the data. The default is no
compression.
The environment object allows you to specify one or more data safety features to ensure the reliability
of the data on your offline tape volumes. You can select one or more of the following
options:
CRC - Performs a Cyclic Redundancy check and writes it for each data block on a tape volume.
This enables detection of a bad block during a restore operation.
FULL_VERIFY - Rereads all saved data and compares to what is on disk during a save. This
option approximately doubles the time for the data copy phase of a save operation.
XOR - If the CRC check detects a bad block during a restore operation, the XOR mechanism
allows recovery of the block. This option is applicable only to data type VMS_FILES, for which
the backup agent is VMS BACKUP.
By default, all three options are enabled for maximum data safety.
The drive count specifies the number of tape drives to use for each save or restore using this
environment. If there are at least as many drives available as the drive count, that number of
drives are allocated for each save and restore request. If not, a reduced number of drives are allocated.
The default and highly recommended value is 1. The number of drives may range from 1 to 32.
3.4.6 Prologue and Epilogue
The prologue and epilogue attributes in the environment allow you to invoke a command procedure
before and/or after the entire save or restore request. This allows you to perform pre-processing
and post-processing operations around the entire request. Compare the order of
Saving and Restoring Data 3–13