System Center Data Protection Manager (SCDPM) is an enterprise-class Microsoft backup solution that helps in protecting many workloads. The configuration of this backup solution is based on Protection Groups. A protection group contains several data sources that share the same configuration such as backup duration (Short-term or Long-term), and retention goal.
DPM can store the backup on disk (disk-to-disk or D2D), on tape library (disk-to-tape or D2T) or to Microsoft Azure (disk-to-cloud or D2C). These supports can be mixed for high availability: so it is possible to perform D2D2D backup, D2D2T, or D2D2C. The best practice about backup is called the 3-2-1 strategy and says that:
- Having at least 3 total copies of your data.
- 2 copies of which are local but on different mediums.
- 1 copy (the third copy) stored offsite.
By default, DPM at midnight checks all existing backups to see if any of those are outside the retention goal based on the number of days you specified when you create a protection group.
In this quick blog post, I will share with you how DPM manages short-term retention goal for protection groups.
How DPM Manages Retention Goal
The way DPM manages retention goal is led by the days you set up when creating or modifying a protection group.
For example, you have a protection group (PG) set for 14 days short-term retention. This doesn’t mean that DPM will start removing backups which are 14 days older, but instead, it will look for 14 days’ worth of successful backups.
To make it simple, let me explain it with the following example:
- You create a protection group (PG) for 10 days retention.
- From day 1 to day 9, all daily backups run successfully.
- On day 10th, there is a backup failure. Due to the current retention goal (10 days), no backups were yet deleted.
- On day 11 the backup runs successfully. At midnight DPM checks all existing backups to see if any of those are outside the retention goal. It finds 10 backups created in distinct days and the protection group goal is 10 distinct days. As those are within the limit. No backups will be removed.
- On day 12 backup failed again. At midnight DPM checks all existing backups to see if any of those are outside the retention goal. It finds 10 backups created in distinct days and the PG goal is 10 distinct days. As those are within the limit. No backups will be removed.
- On day 13 backup ran successfully. At midnight DPM checks all existing backups to see if any of those are outside the retention goal. It finds 11 backups created in distinct days and the PG goal is 10 distinct days. During prune, the backup created on Day 1 will be removed.
With that said, the list below contains 18 backups. The explanation above would lead us to retain 14 but we do have 4 extra backups. The reason is that DPM counts distinct days. So if you have 10 backups created on the same day, then those will count as a single distinct day.
In the following screenshot, I highlighted 4 backups that had run on the same day. Thus that’s why we now have 18 recovery points and not 14.
Also, if there were days where backup didn’t complete successfully, so that day’s backup will be missing and that’s why you will see the oldest backup date being beyond the 14 days retention goal.
Again, DPM does NOT count backup as calendar date in order to remove them but to distinct successfully backups days. Please note that the same concept applies to Microsoft Azure Backup Server as well.
Hope the explanation above shed the light on how DPM manages protection group goal.
Do you want to learn more about System Center Data Protection Manager and how to create a hybrid-cloud backup solution? Make sure to check my recently published book here: Microsoft System Center Data Protection Manager Cookbook.
With this book (over 450 pages) on your side, you will master the world of backup with System Center Data Protection Manager and Microsoft Azure Backup Server deployment and management by learning tips, tricks, and best practices, especially when it comes to advanced-level tasks.
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