Because backups are acquired in units of RDAREAs, both updated pages and unupdated pages are included in a backup. When you use the differential backup facility, only pages updated since the last time a backup was made are included in a new backup. When you make a backup of only the material that differs from the previous backup, the backup processing time is reduced. If the database is large but only a small amount of data has been updated, you should consider using the differential backup facility. The following figure provides an overview of the differential backup facility.

Figure 6-1 Overview of the differential backup facility

Explanation

1. RDAREAs 1 to 3 are backed up on Sunday. All pages in RDAREAs 1 to 3 that are currently in use are backed up. This backup is called a full backup, and the RDAREAs in the group that is backed up are referred to as the differential backup group.
2. Update processing is performed during the workday on Monday.
3. RDAREAs 1 to 3 are backed up after the workday is over on Monday. At this time, only the updated pages in RDAREAs 1 to 3 are backed up. Such a backup is called a differential backup.
4. Update processing is performed during the workday on Tuesday.
5. RDAREAs 1 to 3 are backed up after the workday is over on Tuesday. At this time, only the updated pages in RDAREAs 1 to 3 are backed up.

Recovering the database

For details about recovering the database when you use the differential backup facility, see 21.4 Database recovery using the differential backup facility.

Remarks

You can also use the differential backup facility when operating without unloading the system log.

Notes

• You store all backup files (full backup files, differential backup files, and accumulation-differential backup files) from the same differential backup group on the same server machine. For details about accumulation-differential backup files, see 6.5.4 Creating an accumulation-differential backup.
• A differential backup cannot be made of LOB RDAREAs. Rather, all pages that are in use must be backed up every time a backup is made.
• If the configuration of an RDAREA has changed, a full backup of the RDAREA must be made again. A backup made before an RDAREA's configuration was changed cannot be used to restore the RDAREA.
• You must use the NetBackup linkage facility to back up RDAREAs onto a tape device. If you do not use the NetBackup linkage facility, it will not be possible to back up RDAREAs onto a tape device.