Azure Storage Access Tiers

Azure Blob Storage offers several access tiers that can help you optimize costs by storing your infrequently accessed data in a lower-cost tier. Each tier has different availability, latency, and pricing characteristics.

Understanding Access Tiers

The primary purpose of access tiers is to provide a cost-effective way to manage data based on its access frequency. By selecting the appropriate tier, you can reduce storage costs significantly.

Hot Tier

The Hot tier is optimized for data that is accessed frequently. It offers the lowest access latency and the highest transaction costs.

• Use Case: Frequently accessed data, such as images on a website, active project files, or commonly used documents.
• Pricing: Highest storage cost, lowest access cost, highest rehydration cost (if applicable for standard).

Cool Tier

The Cool tier is intended for data that is accessed infrequently but requires quick access when needed. It has a higher storage cost than Archive, but lower access costs than Hot.

• Use Case: Data that is not accessed regularly but needs to be available within milliseconds, such as recent backups or data for a specific business period.
• Pricing: Lower storage cost than Hot, higher access cost than Hot, lower rehydration cost.
• Minimum duration: Data stored in the Cool tier must be kept for at least 30 days.

Archive Tier

The Archive tier is designed for data that is rarely accessed and stored for compliance or archival purposes. It offers the lowest storage costs but the highest access latency and retrieval costs.

• Use Case: Long-term archival of data, regulatory compliance data, disaster recovery archives where immediate access is not critical.
• Pricing: Lowest storage cost, highest access cost, highest rehydration cost.
• Minimum duration: Data stored in the Archive tier must be kept for at least 180 days.

When to Use Which Tier

Choosing the right access tier depends on your data access patterns and cost considerations.

Rehydration

Retrieving data from the Cool or Archive tiers requires a rehydration operation. This process can take time, and there are associated costs. You can choose between standard and high-priority rehydration. Standard rehydration is less expensive but takes longer, while high-priority rehydration is faster but costs more.

Rehydration Options:

• Standard Rehydration: Typically takes up to 15 hours for Archive tier, and seconds for Cool tier. Lower cost.
• High-Priority Rehydration: Typically takes less than 1 hour for Archive tier, and seconds for Cool tier. Higher cost.

Managing Access Tiers

You can set the default access tier for your storage account, or you can set the access tier for individual blobs. This can be done via the Azure portal, Azure CLI, PowerShell, or programmatically using the Azure Storage SDKs.

Example: Setting Access Tier using Azure CLI

az storage blob set-tier --account-name <your-storage-account-name> ^
    --container-name <your-container-name> ^
    --name <your-blob-name> ^
    --tier Hot

Example: Setting Access Tier using PowerShell

Set-AzStorageBlobContent -Container <your-container-name> -Blob <your-blob-name> -StandardBlobTier Cool -Context <your-storage-context>

Lifecycle Management Policies

Azure Blob Storage lifecycle management policies allow you to automatically transition blobs between access tiers or delete them based on rules you define, such as the age of the blob or the last modification date. This is a powerful tool for automating cost optimization.

Example Rule: Move blobs older than 90 days from Hot to Cool, and blobs older than 365 days from Cool to Archive.