Log Backup Sessions

A sequence of the 15-min (or custom) intervals between the runs of ‘parent’ job comprises a log backup (‘child’ job) session.

• Initial session starts at the moment when ‘parent’ job (image-level backup) schedule was enabled, then session starts with each start of the ‘parent’ job.
• Log backup (‘child’ job) continues working until the next start of the VM image-level backup (‘parent’). At this point, ‘child’ job stops and then starts a new session, performing steps 1-5.
• Session ends just before the next run of the ‘parent’ job, and/or when this ‘parent’ job is disabled (using the menu command or by modifying job schedule).

Assume that VM image-level backup job was configured to run daily at 11:00 PM, starting on May, 5. The figure above illustrates the following course of action:

1. Initial ‘child’ job session starts as soon as ‘parent’ job schedule is enabled (no backups yet) – this happens at 7:00 PM on May, 5. The ‘child’ job remains in the Idle state, waiting for an image-level backup to arrive.
2. At 11:00 PM on May, 5 ‘parent’ job runs on schedule, creating an image-level backup of SQL Server VM.
3. ‘Child’ job state is now Working, and a sequence of log backup intervals follows. If all log backups are successfully transferred to backup repository before the moment when a new session must start, the job will go into the Idle state and wait for remaining log backup interval(s) to expire.
4. At 11:00 PM on May, 6 next run of the ‘parent’ job takes place, and new ‘child’ job session starts.

Transaction log backup requires that at least one image-level backup of SQL Server VM is performed, so remember that:

• Transaction logs for newly appearing databases will be backed up only after the image-level backup of the corresponding SQL Server is performed.
• If a new log backup (‘child’) job session starts when no restore point has been yet created by image-level backup (‘parent’) job, and there are no previous logs to process, ‘child’ job will remain in the idle state, waiting for a new restore point to arrive.

• Transaction log backup will not take place after full SQL Server VM restore.