Understanding the Differences Between Block Blob, Append Blob, and Page Blob in Azure

Introduction

Azure Blob Storage offers three distinct blob types: Block Blob, Append Blob, and Page Blob. Each is designed for specific use cases and workloads. In this blog, we’ll break down these blob types, explain when to use them, and compare their features in a simple and straightforward way.

1. Block Blob

Block Blobs are the most commonly used blob type in Azure. They store unstructured data like text or binary files and are optimized for sequential read and write operations.

Key Features:

• Data Structure: Divided into blocks, where each block can be uploaded or replaced independently.
• Maximum Size: ~190.7 TiB (up to 100,000 blocks of 4 MiB each).
• Access Patterns: Optimized for sequential access.
• Tiers Supported: Hot, Cool, Cold, Archive.

Use Cases:

• Storing large files such as media files (videos, images).
• Backups and restore operations.
• Data lakes for big data analytics.

Example:

If you’re building a video-on-demand platform, Block Blobs are ideal for storing and delivering large media files efficiently.

2. Append Blob

Append Blobs are designed for append-only operations, meaning you can add data to the end of the blob but cannot modify or delete existing data.

Key Features:

• Data Structure: Similar to Block Blobs but optimized for appending data sequentially.
• Maximum Size: Up to 5 TiB.
• Access Patterns: Append-only; no overwrite or random modifications.
• Tiers Supported: Setting access tiers is only supported for block blobs.

Use Cases:

• Logging and telemetry (e.g., application logs, system logs).
• Audit trails for compliance.
• Continuous data streams from IoT devices.

Example:

If you’re building a logging service to collect real-time application logs, Append Blobs are perfect because they allow appending new log entries efficiently.

3. Page Blob

Page Blobs are designed for random read/write operations. Unlike Block and Append Blobs, they are structured to store data in 512-byte pages.

Key Features:

• Data Structure: Divided into fixed-size pages (512 bytes).
• Maximum Size: Up to 8 TiB.
• Access Patterns: Optimized for random read/write access.
• Performance: High IOPS and low latency.
• Tiers Supported: Setting access tiers is only supported for block blobs.

Use Cases:

• Storing Virtual Hard Disks (VHDs) for Azure Virtual Machines.
• Databases with frequent random updates.
• Transactional log files requiring high IOPS.

Example:

If you’re running an Azure Virtual Machine, its OS disk and data disks are stored as Page Blobs because they require fast, random read/write access.  

Comparison Table

When to Use Each Blob Type

1. Use Block Blob When:

   • You need to store large unstructured files (e.g., images, videos, backups).
   • Cost optimization with tiering (Hot, Cool, Cold, Archive) is essential.

2. Use Append Blob When:

   • Your workload involves appending data sequentially, such as logging or telemetry.
   • Data modification is unnecessary.

3. Use Page Blob When:

   • You need low-latency random access to data.
   • Your workload involves virtual disks (e.g., Azure VMs) or databases.

How to Create Block Blob, Append Blob, and Page Blob

Mapping Types to Kinds

Key Takeaways

• Block Blobs are ideal for general-purpose object storage.
• Append Blobs are specialized for sequential logging and telemetry.
• Page Blobs provide disk-like functionality for workloads requiring random read/write operations.

By selecting the right storage account type (Standard or Premium) and kind (General Purpose v2, Block Blob Storage), you can ensure your Azure storage is perfectly aligned with your application’s requirements.