Understanding Access Tiers in Azure Blob Storage

Introduction

Azure Blob Storage offers access tiers to help us manage our data storage costs based on how frequently our data is accessed. By selecting the right tier, we can optimize our expenses while ensuring our data is available when needed. Let’s dive into these tiers, how to set them, and where they can be configured.

Azure Blob Storage Access Tiers

1. Hot Tier

• Purpose: For data that is accessed or modified frequently.
• Cost Characteristics:
  • Higher storage costs compared to other tiers.
  • Lower access costs (retrieval and transaction costs).
• Use Cases:
  • Active application data.
  • Real-time analytics and frequently accessed datasets.

2. Cool Tier

• Purpose: For data that is infrequently accessed but still requires fast retrieval.
• Cost Characteristics:
  • Lower storage costs than Hot.
  • Higher access costs than Hot.
• Minimum Retention Period: 30 days.
• Use Cases:
  • Backup and disaster recovery.
  • Older but still-needed data that may occasionally be accessed.

3. Cold Tier

• Purpose: For data that is rarely accessed and must be stored for at least 90 days.
• Cost Characteristics:
  • Even lower storage costs than Cool.
  • Higher access and transaction costs compared to Hot and Cool.
• Minimum Retention Period: 90 days.
• Use Cases:
  • Long-term backups.
  • Rarely accessed compliance data that needs to be available immediately.

4. Archive Tier

• Purpose: For data that is almost never accessed and can tolerate delays in retrieval.
• Cost Characteristics:
  • Lowest storage costs.
  • Highest access costs, with additional charges and delays for data rehydration.
• Rehydration Times:
  • Retrieval times can take hours (standard priority) or minutes (high priority).
• Minimum Retention Period: 180 days.
• Use Cases:
  • Long-term archival and compliance data.
  • Historical records or logs with no immediate access needs.

Comparison of Access Tiers

Tier	Access Frequency	Storage Cost	Access Cost	Minimum Retention Period	Use Cases
Hot	Frequent	High	Low	None	Active datasets, real-time analytics.
Cool	Infrequent	Lower than Hot	Higher than Hot	30 days	Backups, disaster recovery.
Cold	Rare	Lower than Cool	Higher than Cool	90 days	Long-term backups, compliance data.
Archive	Almost Never	Lowest	Highest	180 days	Historical data, regulatory archives.

 

Where Can You Set Access Tiers?

1. At the Storage Account Level

When you create a StorageV2 (General Purpose v2) account, you can set the default access tier for all Block Blobs within that account. The available options are Hot, Cool, and Cold.

• Steps:
  1. Go to the Azure Portal.
  2. Click on Create a resource and select Storage Account.
  3. Under the Advanced tab, choose the default access tier:
     • Hot: For frequently accessed data.
     • Cool: For infrequently accessed data stored for at least 30 days.
     • Cold: For rarely accessed data stored for at least 90 days.
  4. Complete the setup and create the storage account.

2. At the Blob Container Level

The default tier set at the storage account level applies to all containers by default. However, you can override the tier for specific containers if needed.

• Steps:
  • When creating a new container, the access tier is inherited from the storage account unless manually overridden.
  • Navigate to the container settings in the Azure Portal to modify the tier for existing blobs as needed.

3. At the Individual Blob Level

You can set or change the access tier of specific blobs at any time. This allows for granular control of storage costs and performance.

• Steps in Azure Portal:
  1. Navigate to the storage account.
  2. Go to the Blob service section and select the container containing your blob.
  3. Select the blob you want to modify.
  4. Click on Change tier and choose between Hot, Cool, Cold, or Archive.

We can also set the access tiers from CLI.

How to Choose the Right Tier

1. Determine Data Access Frequency:
   • Frequently accessed? Use Hot.
   • Rarely accessed? Consider Cool, Cold, or Archive.
2. Consider Retention Periods:
   • Data stored in the Cool tier must remain for 30 days.
   • Data stored in the Cold tier must remain for 90 days.
   • Data stored in the Archive tier must remain for 180 days.
3. Use Lifecycle Management:
   • Azure provides lifecycle policies to automatically transition blobs between tiers based on access patterns and age.

Key Takeaways

• Access tiers (Hot, Cool, Cold, and Archive) are only available for Block Blobs.
• You can set default tiers at the account level, apply overrides at the container level, or configure tiers for individual blobs.
• Use Hot for active data, Cool for infrequent access, Cold for rarely accessed but readily available data, and Archive for long-term storage with retrieval delays.
• We can make use of lifecycle management to automatically transition from one access tier to another.

This flexibility ensures you can optimize your storage costs while meeting your performance and accessibility needs.

See also

The blog post: Understanding the archive tier of azure storage accounts