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I saw a blog of Incremental backups on Microsoft Azure Backup: Save on long term storage. (https://azure.microsoft.com/ja-jp/blog/microsoft-azure-backup-save-on-long-term-storage/) But I have some questions about the Azure Backup Retention rang process works.

As an example, let us take a data source, A, made up of blocks A1, A2, … A10, which needs to be backed up monthly. Block A2, A3, A4, A9 change in the first month, and A5 changes the next month.

When I set the backup retention range of two months, so after I finished the third backup, can I restore block A10? If I can, can you tell me the process? Because as I know, the data source without change had been deleted. If it not deleted, as the picture shows, there will have two blocks A2 (the first backup and the second backup)? If this is right, the Total Space occupied will continue to increase.

Arthur
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In Azure backup, first backup is always a full backup and the subsequent backups are incremental in nature.

For example: 1st day full backup (100 GB) on premise to Azure = Successful 2nd day only the changes/ churn rate will be backed up as incremental. Could be 10 GB churn rate/changes as compared to previous day. Likewise this will continue till the 7th day. On 8th day as per the retention policy, the first day recovery point gets deleted and the full backup is merged with the 2nd day incremental backup which becomes the oldest recovery point for you to recover your data. For this day if you restore you will get 100 GB data. Because there was no additional data added to the full backup just the changes within 100 GB were backed up as incremental on the 2nd day.

This same logic applies in your use case as well.

Hope this clarifies!

Let me know if this is confusing or you've additional questions for me that I can help with.

SadiqhAhmed-MSFT
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  • I can't understand the process of the merged very well, do you know some documents about this technology, and can I understand like that when full backup is merged with the 2nd day, the old dates which changes/ churn rate on the 2nd day will cover the old dates ? But if the changes/ churn rate on the 2nd day is additional data added to 1st day, it will change like below: (1st day: Full Backup 100GB → 2nd day: 10GB changed different to 100GB → On 7th day: the 2nd day recovery point just keep 10 GB→ On 8th day: the 2nd day recovery point increase to 110GB)? thanks – Arthur Oct 16 '19 at 06:35
  • @jason ye has detailed post on backup retention here - https://stackoverflow.com/questions/45914855/azure-backup-and-how-retention-policies-are-executed – SadiqhAhmed-MSFT Nov 05 '19 at 11:32