A file called the differential backup management file is output whenever a backup is made. This file stores information about the differential backup, which is used while the backup is being made and when the backup is used by HiRDB for database restoration.

You use the pdfmkfs command to create a HiRDB file system area for storing differential backup management files; for a HiRDB parallel server configuration, you must create the HiRDB file system area in the unit in which the system manager is defined:

 
pdfmkfs -n 10 -l 4096 -e 60000 -k UTL /pdcopy/admfile
 

Explanation

-n: Specifies in megabytes the size of the HiRDB file system area.

-l: Specifies the maximum number of files.

-e: Specifies the number of increments.

-k: Specifies the purpose of the HiRDB file system area (a HiRDB file system area for utilities).

/pdcopy/admfile:

Specifies a name for the HiRDB file system area. Differential backup management files will be created in this HiRDB file system area. The name of the differential backup management file is the same as the backup group name.

Notes

• Differential backup management files are important files because they contain information about the differential backups that are made. Without these files, the differential backup facility cannot be used and the database cannot be restored. For this reason, it is important not to delete this HiRDB file system area or the differential backup management files it contains. Each time a backup is made, you can use the pdfbkup command to back up the differential backup management files.
• When the system switchover facility is being used, you must create this HiRDB file system area (as a character special file) on the hard disk that is shared by the primary and secondary systems. If the HiRDB file system area is created as a regular file, the following steps must be taken:

Procedure

1. Create HiRDB file system areas with the same name in the primary and secondary systems.
2. Each time a backup is made, use the pdfbkup command to back up the differential backup management files.
3. Use ftp or some other transfer method to copy into the secondary system the backup of the differential backup management files that you created in step 2.
4. Use the pdfrstr command to restore the differential backup management files in the secondary system.

Remarks

Backup files and differential backup management files can be stored in the same HiRDB file system area.

A group of RDAREAs to which the differential backup facility is applied is called a differential backup group. This section explains how to group RDAREAs.

(a) Restoring RDAREAs to the most recent differential backup acquisition point, or restoring RDAREAs using an unload log file (system log files)

In this case, it is possible to restore a specific RDAREA in a differential backup group. When the database contains a large amount of data, grouping all RDAREAs together for the purpose of making backups makes it time-consuming to restore a specific RDAREA. This is because of the amount of time required to load the backup files sequentially.

Therefore, we recommend grouping RDAREAs into manageable groups and making backups by group. For example, when a disk error occurs, RDAREAs are restored one disk at a time. Therefore, the RDAREAs stored on the same disk can constitute a group.

(b) Restoring RDAREAs to other than the most recent differential backup acquisition point (restoring RDAREAs using only full backup files)

In this case, it is not possible to restore a specific RDAREA in a differential backup group. All RDAREAs in the group must be restored.

Therefore, we recommend that RDAREAs that are related constitute each group. For example, one group of RDAREAs might store the data of the same table, while another group of RDAREAs might store the indexes for this table. In this way, both the RDAREAs for the table and the RDAREAs for the indexes can be restored at the same time with a single execution of the pdrstr command.

Notes

When RDAREAs are restored to other than the most recent differential backup acquisition point by using only the full backup files, the information for differential backups subsequent to the restoration point in the differential backup management files becomes invalid. Consequently, it will not be possible to restore RDAREAs to the most recent differential backup acquisition point. Note that differential backup information is not invalidated when an error occurs during restoration.