How NBPEM (NetBackup Policy Execution Manager) schedules a frequency backup.

Problem

This article contains a brief description of PEM2 (NBPEM Second Generation) operation introduced with the NetBackup <6.5.2> release.

Example scenario:

A frequency schedule is set to run once a day or every 24 hours.

The first backup started at 0400 as scheduled with an open window but all subsequent backups start at midnight when the next open window begins at midnight.

The frequency of 24 hours or 1 day is not honored when the next open window begins at midnight.

The expectation is that all backups will start at 0400, once a day or every 24 hours, regardless of the open window start time.

Error Message

No error message is recorded.

Cause

The scheduler NBPEM calculates the start time of the backup from the start of the open window.

In the first example, (Image 1) a frequency backup runs daily with an open window between 0400 and 0800, Sunday through Saturday.

In a traditional sense this schedule has open windows with clearly defined start and end times.

Image 1:

In a second example (Image 2), the weekday open window starts at 0400 and ends at 0800, Monday through Friday.

The weekend open window starts at midnight and is a continuous block that covers more than one day, Saturday and Sunday.

For this schedule, the M-F backup is scheduled to start at 0400. However the Saturday and Sunday Backup will not start at 0400 but start just after midnight on Saturday and Sunday, or at the beginning of the open window.

Image 2:

In the last example (Image 3), the open window starts at 0400 Sunday and is a continuous block until 2400 Saturday.

For this schedule the backup will start at 0400 and run daily at 0400. The start of the backup is defined by the start time of the open window. In this case the open window starts Sunday at 0400 and ends Saturday at 2400.

Image 3:

Solution

The scheduler will start the backup at the start of the open window to avoid scheduler creep.

Scheduler creep was a phenomenon in previous versions of NetBackup. A scheduled backup could creep forward in time during an open window until the backup start time extended beyond the window and the backup was skipped. Take the first example above:

If a backup is scheduled to start at 0400 but doesn't go active until 0700 while waiting for resources and completes successfully, the next scheduled backup, based upon a frequency of 24 hours or 1 day, will be scheduled to start at 0700 the following day.

Note: The schedule is not calculated from the backup stop time but from when it started.

If the backup, which is scheduled to start at 0700 waits another three hours for resources, the backup will not start before the open window closes at 0800.

The result is a failed backup: Status Code 196 - client backup was not attempted because backup window closed.

To avoid schedule creep, NBPEM will schedule the backup to start at the beginning of the open window, and not from the previous start time.