What is Blob Storage?

Blob storage enables companies to keep large amounts of data secured and stored within a Microsoft Azure storage account. Blob storage is a convenient, cost-effective and highly scalable cloud-based method of object storage.

In this guide, we’ll dive into the basics of blob storage, the three primary types of blobs, and the three primary pricing tiers. 

Basics of Blob Storage

A blob (Binary Large Object) consists of binary data stored as a single item. While data can be of any type, blob storage is particularly useful for storing media, such as audio and video, and frequently changing data, such as log files.

Applications that benefit from blob storage (a type of object storage) include:

  • Online media sharing, e.g., accessing images or videos directly through a browser.
  • Media streaming, whether audio or video.
  • Distributed file access.
  • Log file storage and update.
  • Disaster recovery, including backup, archival and restoration.
  • Massive data set storage, including data used for analytical applications. 
  • IoT (Internet of Things) applications.

Blobs are stored in containers – the basic storage unit for a Microsoft Azure storage account. Containers may represent specific file types – images, for example, may be stored in one container, while video files are stored in another. Containers can be analogized to folders within a directory structure. Individual Azure storage accounts can contain up to 500 TB of data.

Blob storage allows for access from anywhere in the world via the internet. A wide variety of languages can be used to access blob storage, including Go, Java, .NET, Node.js, PHP, Python, and Ruby. While Microsoft has its own strong cybersecurity structures in place for the Azure platform, it also offers specific security recommendations for blob storage users. 

Applying Microsoft’s security recommendations allows organizations using blob storage to streamline their cybersecurity operations and have fewer concerns regarding vulnerability management. According to cloud computing expert Barbara Ericson of Cloud Defense, “Knowing how to accurately identify vulnerabilities in your organization and correct them to prevent future malicious intrusions or data breaches is vital if you want to maintain operational security for the long-term future.”

Types of Blobs

There are three primary blob types: append, block, and page blobs.

Append Blobs

Also consisting of blocks, append blobs are specifically designed for use with append operations. The most common use of an append blob is for storage and updating of log files. Blocks may be appended to the end of an append blob, but previously existing blocks may not be modified or deleted.

Just as with block blobs, an append blob may contain up to 50,000 blocks, each up to 4 MiB.

Block Blobs

Block blobs are subdivided into blocks and are primarily intended for storage of media files, documents, text files, and binary files. Blocks can be of varying sizes, with a maximum size of 4000 MiB (mebibytes) per block (in the most current Azure version). There may be anywhere up to 50,000 blocks per blob, giving a maximum block blob size of around 4.75 TiB (tebibytes).  

Individual blocks within a block blob can be modified or replaced, and blocks can be added to or deleted from the block blob. Parallel uploading of individual blocks optimizes the upload time for block blobs as well.

Page Blobs

A page blob is intended for read and write operations. A page blob is an assembly of 512-byte pages, with a maximum page blob size of 8TiB. Page blobs are useful for storage of items such as operating systems and disaster recovery data.

Also take note that all blobs, regardless of type, come encrypted due to the fact that they are cloud-based. Cloud encryption in general will encode data when it travels between cloud-based storage or applications and to users at their respective locations. 

According to Toronto-based software developer Gary Stevens of Hosting Canada, the cloud remains one of the most secure methods for storing your data online, explaining “More and more individuals and malicious groups are out there, trying to steal and sell your data. Thankfully, due to so many protective services, the cloud is incredibly difficult to hack. Under the maintenance of a third-party administrator, users save data to an off-site, remote database storage system. The middle-man is the Internet, which serves as the connecting thread between you and the computer administrator.”

Pricing Tiers for Blob Storage

There are two types of costs associated with blob storage: transaction costs (i.e. costs for accessing the data) and storage costs. Transaction costs are per block, that is a write operation on one block is a single transaction.

Blob storage pricing is divided into tiers, based on the frequency of access to the data. This allows for more cost-efficient storage, particularly where the user has large amounts of data that require very infrequent access. 


Hot storage is for the most frequently accessed data. It has the highest storage cost but the lowest storage cost of the three tiers. Hot blob storage is always online.


Cool storage is for data that is periodically accessed, but not with great frequency. Specifically, cool storage is appropriate when data is not accessed more than once every 30 days. Cool storage has a lower storage cost than hot storage, but higher transaction costs. As with hot storage, cool storage data is always online.


Archival storage is for data that requires long-term storage and very infrequent access (i.e. less than once every 180 days). It has the lowest storage cost and the highest transactional cost. Archival data storage is always offline. Users can optimize their costs through use of data lifecycle policies. 

Nahla Davies
Nahla Davies
Nahla Davies is a software developer and writer. Before devoting her work full time to technical writing, she managed—among other intriguing things—to serve as a lead programmer at an Inc. 5,000 experiential branding organization whose clients include Samsung, Time Warner, Netflix, and Sony.

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