The backup unit is specified in an option of the database copy utility. Data can be backed up in the following units:

• By system (all RDAREAs)
• By unit (all RDAREAs in a unit)^#
• By server (all RDAREAs in a server)^#
• By RDAREA (individual RDAREAs)

#: Function applicable to HiRDB parallel server configurations only.

We recommend that you back up data on a regular basis. You must back up data before performing the tasks listed below. If you do not back up data at these times, you will not be able to restore the database to the most recent synchronization point in the event of an error.

• Before and after executing a UAP or utility in the no-log mode
• Before and after executing a UAP or utility in the pre-update log acquisition mode
• After executing the database structure modification utility on an RDAREA. Do so also before moving an RDAREA
• After performing restoration using system logs
• Before performing restoration using only unload log files
• Before and after installing a new version of HiRDB
• After registering a plug-in (after executing the pdplgrgst command)
• After stopping use of a plug-in (after deleting the pdplugin operand)
• After making an RDAREA resident in memory or after synchronizing the in-memory data buffer with the in-memory RDAREA

Backing up data at the following times can shorten the time required for restoring the database should an error occur:

• After executing a process that needs to back up the system RDAREA
  Processes that need to back up the system RDAREA are those processes that need to back up the master directory RDAREA, data directory RDAREA, or data dictionary RDAREA in Table 6-3 RDAREAs to be backed up together.
  
• After updating a large amount of table data

A backup file can be created in any server machine on which HiRDB is running. There is no requirement that a backup file be created in the same server machine where the RDAREAs being backed up are located. A server machine containing a device such as CMT or DAT might be used.

The server machine to be used to store a backup file can be specified in an option of the database copy utility (pdcopy command).

When an RDAREA is backed up without using the database copy utility, the following must be completed before the backup operation is started:

• Use the pdhold -c command to place the RDAREA in shutdown and closed status.
• Use the pdhold -b command to place the RDAREA in backup-hold status.
• Terminate HiRDB normally.

List RDAREAs cannot be backed up. There is no need to make such backups, because lists can be re-created easily as long as the tables used for the lists are available.

If a character special file is used for a backup file, the character special file must be placed in a HiRDB file system area for utilities. To do this, UTL must be specified in the -k option of the pdfmkfs command.

If a message reporting a disk space shortage is output during execution of the database copy utility even though ample disk space has been provided, the following are possible causes:

• The maximum kernel parameter value has been exceeded.

Change the kernel parameter value. You can also avoid the problem by creating multiple backup files. However, if the OS does not support large files, you must keep the disk partition size to 2 GB or smaller to be able to handle multiple files.

You can use the pdbkupls command to check the backup information collected by the database copy utility. For example, you can check the information listed below (for details about the information that can be checked, see the manual HiRDB Version 9 Command Reference):

• Backup acquisition date
• Names of RDAREAs for which backup was collected
• Value specified for the backup acquisition mode (-M option)