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Veritas NetBackup™ Administrator's Guide, Volume I

Last Published: 2019-07-01

Product(s): NetBackup (8.2)

About backup frequency

To determine backup frequency, consider how often data changes. For example, determine if files change several times a day, once a day, weekly, or monthly.

Typically, sites perform daily backups to preserve daily work. Daily backups ensure that only one day's work is lost in case of a disk failure. More frequent backups are necessary when important data changes many times during the day and the changes would be difficult to reconstruct.

Daily backups are usually the incremental backups that record the changes since the last incremental or full backup. Incremental backups conserve resources because they use less storage and take less time to perform than full backups.

Full backups usually occur less frequently than incremental backups but should occur often enough to avoid accumulating consecutive incremental backups. A large number of incremental backups between full backups increases the time it takes to restore a file. The time increases because of the effort that is required to merge the incremental backups when files and directories upon restore.

Consider the following when setting the frequency for full backups:

Extend the time between full backups for the files that seldom change. A longer frequency uses fewer system resources. It also does not significantly increase recovery time because the incremental backups between full backups are smaller.
Decrease the time between full backups for the files that change frequently. A shorter frequency decreases restore time. A shorter time between full backups can also use fewer resources. It reduces the cumulative effect of the longer incremental backups that are necessary to keep up with frequent changes in the files.

To achieve the most efficient use of resources, ensure that most of the files in a given policy change at about the same rate. For example, assume that half of the files in a policy selection list change frequently enough to require a full backup every week. However, the remaining files seldom change and require monthly full backups only. If all the files are in the same policy, full backups are performed weekly on all the files. This wastes system resources because half the files need full backups only once a month. A better approach is to divide the backups into two policies, each with the appropriate backup schedule, or to use synthetic backups.

If more than one automatic schedule is due for a client within a policy, the backup frequency determines the schedule that NetBackup uses as follows:

Jobs from the schedule with the lower frequency (longer period between backups) always have higher priority. For example, a schedule that has a backup frequency of one month takes priority over a schedule with a backup frequency of 2 weeks.
When two schedules are each due to run, the schedule with the schedule name that is first in alphabetical order runs first. Alphabetical priority occurs if both of the following are true:
- Each schedule is within the defined time window.
- Each schedule is configured with the same frequency value.

NetBackup prioritizes the example schedules in the following order:

Table: Examples of schedule frequency and priority

Schedule Name	Frequency	Priority
monthly_full	One month	First
weekly_full	One week	Second
daily_incremental	One day	Third