Basics – Force incremental

In one of those “old dogs can learn new tricks” scenarios, or perhaps more correctly, “never believe it until you’ve read it in the manual”, I recently learnt what force incremental really does in NetWorker groups. I remember sitting in a training course over a decade ago being told, “If you turn force incremental on and the group re-runs on the same day as it would have run a full, it’ll run an incremental”. And that’s what I’d been working on ever since*.

Except, that’s not the way the documentation describes how and what force incremental does. (And that included going back to the man pages for NetWorker 6.1.3, which I still have laying around on a lab client.)

If you’ve not seen the setting before, here it is in the group controls:

Force Incremental is somewhat more targeted than this. In fact, for traditional groups with a 24 hour interval, it won’t do a thing.

The force incremental setting exists for groups that have a shorter than 24 hour interval window. Consider for instance archive log backup groups. You’ll see these every now and then, where they run every 6 hours or so to collect and save any archive logs generated on a particular critical database server. In this sort of scenario, you’ll typically want the first backup of the day to be a full (to pick up all the log files), then each subsequent backup during the day to be an incremental (to grab the files created between the previous backup and the current one). In that sense, it’s a microcosm of a traditional weekly-full/daily-incremental backup regime, just conducted over the course of a single day.

To that end, the scheduling setup for such a group might resemble the following:

The first part, shown above, is straight forward – the group should be enabled to automatically start, and given a suitable start time. In this scenario, I’ve given it a start time of 04:00.

In the Advanced tab for the group, the Level field is used to set an initial level of each day to full, the interval is set to 06:00, meaning the group will automatically re-run every 6 hours after 4am, and the force incremental option is enabled to make each subsequent backup after the 4am one an incremental backup.

With this configuration, the group execution would be as follows:

• 04:00 – full
• 10:00 – incr
• 16:00 – incr
• 22:00 – incr

You might be wondering what the advantage of force incremental is: after all, this could be readily accommodated by using different groups that start at each of 04:00, 10:00, 16:00 and 22:00, but therein is your answer: this process collapses 4 groups down to 1, making management of what is effectively a single task considerably easier.

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* Given I’m relatively sure I’ve seen force incremental working in the originally described manner, I’m assuming it might have done so (perhaps accidentally) in v5.x.