When you create a server backup plan and select a backup destination, you can choose to enable extended retention rules in addition to specifying a retention period.
Extended retention rules allow you to keep specific full (or synthetic full) backups for an additional period of time.
An extended retention allows you to keep incrementals following a full backup jobs from a source copy when fulls are committed or synthetic fulls complete with errors.
Extended retention rules can be used in the following circumstances:
If you have a single drive tape library
If you want to create a hierarchical retention scheme (grandfather-father-son tape rotation)
Extended retention rules allow you to define three additional "extended" retention periods for full (or synthetic full) backups.
You may want to retain your weekly full backups for 30 days.
You may want to retain your monthly full backup for 90 days.
You may want to retain your yearly full backup for 365 days.
A backup job will be selected for extended retention based on its start time. For example: If a backup job starts at 11:55 pm on August 31st and ends at 1 am on September 1st, then it will be selected as the last full backup for the month of August and will be picked up for extended retention.
In all other cases, we recommend you to use Auxiliary Copy for extended storage as it actually creates another physical copy of the data, thereby reducing the risk of data loss due to media failure.