The following concepts are critical to designing and implementing a successful backup strategy:
- --> Balanced table spaces are the primary factor
- --> Difference between system managed space (SMS) and database managed space (DMS) tablespaces
- --> What pages are included in an incremental or delta backup
Balanced tablespaces:
1. For good backup performance we must make sure that data should be evenly distributed between the tablespaces.
2. In the backup process the db2bm process will be assigned to each tablespace separately. So, if the data in the database is stored in large amount in a single tablespace will cause the other serialisation.
3. If the data evenly distributed between the multiple tablespaces the maximum parallelism will be done throughout the backup.
Difference between SMS and DMS tablespaces:
1. All the pages in the SMS table spaces are backed up when we perform a backup.
2. The pages that are marked as Used will be backed up while backing up DMS table spaces.
What pages that are included in an incremental or delta backup:
1. The pages that are modified since the last full backup will be backed up in incremental backup.
2. A delta backup includes the pages that are modified since the last backup of any type.
3. The LOB, long varchar, and longgraphic(LONG) are also included in the above two backups.
4. If we perform one of the above backups, DB2 keeps track of modified pages since the last backup. If a tablespace has no modified pages since the last backup this will be skipped. At the same time if a tablespace has a single modified page then the the entire tablespaces will be scanned and this will cause that the db2med process to stay in idle state for long time.
5. Incremental and delta backups are designed to be smaller than full backup, but not faster.
6. In some cases these backups are fast, where the scanning of tablespaces were skipped. Otherwise the incremental or delta backup will take longer time than full backup.
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