Understanding the Azure Backup Estimate Calculator

Question

I'm trying to leverage the Azure Backup Estimate Calculator found on the Azure Backup Pricing page at https://learn.microsoft.com/en-us/azure/backup/azure-backup-pricing.

I'm struggling to understand the estimate generator behavior. Scenario:

I set the size of the server to be backed up to 500 GB

I set the "Total number of on-premises servers" to 1

In the column for "Average Monthly #Protected Instances" it displays 1 (this I expect)

If I change the total size of the server to be backed up to 501 GB the "Average Monthly #Protected Instances" changes from 1 to 2. (this I don't expect)

Can someone explain how the spreadsheet calculates that "Average Monthly #Protected Instances" number?

Thanks in advance!

Answer 1

The behavior you observed in the Azure Backup Estimate Calculator is based on the way Azure defines and bills protected instances for backups

Protected Instances: Azure Backup defines a "protected instance" as a unique server or workload (e.g., VM, database, or file share) that is being backed up. The number of protected instances and their sizes directly impact billing.

Azure categorizes protected instances into size tiers, and these tiers determine how many "protected instances" a particular server contributes to billing. The key size tiers are:

1. 0–50 GB: Each instance in this range counts as 1 protected instance.
2. 51–500 GB: Each instance in this range also counts as 1 protected instance.
3. 501 GB–1,000 GB: Each instance in this range counts as 2 protected instances.
4. > 1,000 GB: Larger sizes are divided into additional instances, with each 500 GB increment adding another instance.

Scenario 1: 500 GB Server

• The server's size is 500 GB, which falls within the 51–500 GB tier.
• This counts as 1 protected instance.

Scenario 2: 501 GB Server

• The server's size is 501 GB, which moves it into the 501 GB–1,000 GB tier.
• This tier counts the server as 2 protected instances because it exceeds the 500 GB threshold.

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hth

Marcin