Understanding Azure Blob Storage Access Tiers

Azure Blob Storage offers different access tiers to optimize storage costs for data with varying access patterns. Each tier provides different levels of availability, latency, and cost. Choosing the right access tier can significantly reduce your storage expenses.

Available Access Tiers

Azure Blob Storage supports the following access tiers:

Tier Description Latency Availability Cost (Storage) Cost (Access) Use Cases
Hot Optimized for frequently accessed data. Low (milliseconds) High (99.9% SLA) Highest Lowest Frequently accessed data, active analytics, temporary files.
Cool Optimized for infrequently accessed data. Millisecond to second High (99.9% SLA) Lower than Hot Higher than Hot Infrequently accessed data, older backups, historical data.
Archive Optimized for rarely accessed data with flexible latency requirements. Hours (retrieval time) Low (99.9% SLA for data durability, retrieval time varies) Lowest Highest Long-term archival, disaster recovery, compliance data.

When to Use Which Tier

Hot Tier

Use the Hot tier for data that is actively being used or accessed frequently. This tier offers the lowest access latency and the lowest transaction costs, making it ideal for:

  • Serving images and text for websites.
  • Storing data for real-time analytics.
  • Caching frequently used data.

Cool Tier

The Cool tier is suitable for data that is accessed less frequently but needs to be readily available for a moderate cost. Data stored in the Cool tier can be accessed within milliseconds to seconds. This tier is a good choice for:

  • Storing backups that are accessed periodically.
  • Holding historical data that might be needed for ad-hoc analysis.
  • Content that is accessed less often than in the Hot tier.
Note: Data stored in the Cool tier incurs higher access costs than data in the Hot tier. Consider the retrieval frequency when choosing this tier.

Archive Tier

The Archive tier is designed for data that is rarely accessed and can tolerate retrieval times of several hours. This tier offers the lowest storage costs but has the highest access costs and retrieval latency. It's ideal for:

  • Long-term data archiving for compliance or regulatory purposes.
  • Disaster recovery data that is not expected to be accessed frequently.
  • Archiving old project data that might need to be referenced years later.
Important: Retrieving data from the Archive tier can take hours. Data is also subject to a minimum storage duration policy (typically 180 days).

Changing Access Tiers

You can change the access tier of a blob at any time. When you move data from a cooler tier to a hotter tier (e.g., from Cool to Hot), the change takes effect almost immediately, and you are charged the Hot tier storage rate going forward. There are no egress fees for moving data between tiers within the same region. If you move data from a hotter tier to a cooler tier (e.g., from Hot to Cool), you are charged the cooler tier storage rate, but there may be early deletion charges if the data is deleted before the minimum retention period for the cooler tier.

You can change access tiers using:

  • The Azure portal
  • Azure CLI
  • Azure PowerShell
  • Azure Storage SDKs

Key Considerations

  • Access Frequency: How often do you expect to read or write to the data?
  • Latency Requirements: How quickly do you need to access the data when requested?
  • Cost Optimization: Balance storage costs against access costs.
  • Minimum Storage Duration: Archive tier has a minimum storage duration, and early deletion incurs charges.
[Conceptual Diagram of Access Tiers - Would show flow and cost trade-offs]

By strategically applying access tiers to your blob data, you can achieve significant cost savings while ensuring your data remains accessible according to your operational needs.