Configuring Different Master-Delta Chain Lengths
Summary
The default DS-System master-delta chain setting of 9 is sufficient for most fresh installations of DS-System. This value is used when the Optimization Task runs (on schedule or on demand) to correct the delta chain length for a backup file's generations.
Once a DS-Client starts sending deltas for a file (after initial backup of a file), it will normally only send deltas to keep the backup times as short as possible. This means the DS-System must regularly run an optimization on the backup files to rebuild a master when any backup file's delta chain has passed its configured limit.
At minimum, a periodic optimization should be scheduled to run on all the modified directories on the DS-System.
- Note: It is important to remember the point of the delta chain length is to set a limit that balances the backup (space) efficiency of the deltas with the restore performance of having a full master and a shorter delta chain.
Configuring different Master-Delta Chain lengths requires knowledge about the kind of data being backed up from individual DS-Clients.
The ability to customize Master-Delta Chain configurations is essentially unlimited. Service Providers can create new configurations for specific DS-Clients, or more generally for specific customers or the entire DS-System.
- Remember: The most specific delta chain setting is at DS-Client level (only one setting can apply per DS-Client). This overrides any Customer level configuration, which itself overrides the global default setting for the DS-System. The global default applies in the absence of any other configuration.
The following examples are a starting point from which Service Providers can tailor their DS-System data's delta chain lengths.
Example 1: Big database backups (e.g. DB2, Exchange, SQL server)
You can create specific Delta Chain Configurations for each database backup set type, or group them together in a 'Big Databases' Configuration. Some considerations to make:
- Individual database size (stored size), average size of each delta.
- Average time required to perform Master reconstruction.
- Restore performance required by customer (longer delta chain = slower restore performance; tradeoff is less total stored size).
Example 2: Replication DS-Systems
Replication DS-Systems only receive deltas. Therefore at least one optimization task must be scheduled to periodically fix the delta chain(s).
See Also
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