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Veritas NetBackup™ Administrator's Guide, Volume I

Last Published: 2019-07-01

Product(s): NetBackup (8.2)

How NetBackup determines which schedule to run next

When a policy contains one schedule, the schedule that is selected to run next is straightforward. But when a policy contains multiple schedules, choosing which schedule to run next can become more complicated.

NetBackup performs the following tasks to determine which schedule to run next:

NetBackup determines the due time for each schedule. The due time depends on the following:
- The last backup data for each schedule based on comparable schedules.
- The frequency that is added to each schedule to determine which schedule is due next.
NetBackup checks the start time for each schedule. The schedule with the soonest start time runs next. That is, the schedule with the next open window.

Figure: Schedule selection overview

When any of the following events occurs, NetBackup recalculates which schedule to run next in a policy:

A backup job finishes.
A client backup image expires.
The Policy Execution Manager (nbpem) starts.
The administrator changes the policy.
NetBackup looks for updated policies every 10 minutes. If the policy has recently been updated, NetBackup waits an additional minute to be sure that changes are not currently underway. You can change the frequency that NetBackup looks for updates by changing the Policy Update Interval in the Global Attributes host properties.
See Global Attributes properties.

The due time for each schedule equals the last backup data for the schedule, plus the schedule's frequency:

Due time = Last backup data + Frequency

Last backup data refers to the schedule that ran most recently among comparable schedules. NetBackup uses the date and time of that schedule to determine the due time for all the schedules that use that schedule as the last backup data.

In some cases, the last backup data for a schedule names the schedule itself. In other cases, the last backup data for a schedule is another comparable schedule.

NetBackup makes the following comparisons to identify a comparable schedule:

Full schedules	Compared to other full schedules of the same or longer frequency.
Cumulative incremental schedules	Compared to the following: Full schedules of the same or longer frequency. Other cumulative incremental schedules of the same or longer frequency.
Differential incremental schedules	Compared to the following: Full schedules of the same or longer frequency. Cumulative incremental schedules of the same or longer frequency. Other differential incremental schedules of the same or longer frequency. Note: To have a longer frequency means that the schedule is configured to run less often.

The comparison rules ensure that no schedule is overlooked for consideration, potentially causing a gap in backup coverage.

Figure: Schedule coverage

The following jobs create additional complexities in scheduling:

Multistreaming jobs	Each stream is scheduled independently. The data may change in the time between the streamed backups. Two restores that are based on the same backup may not be identical if created from different streams.
Synthetic backup jobs	NetBackup uses the previous synthetic job as the basis for determing when the next synthetic job should run.