What is Windows Azure Blob Storage

Windows Azure BLOB storage service is used to store and retrieve Binary Large Objects (BLOBs). BLOBs are also simply referred to as files. In this introduction to the Windows Azure BLOB Storage service we will cover the difference between the types of BLOBs you can store,

There are many reasons why using Azure BLOB storage could make sense for your organization. Sharing files with clients, or off-loading static content from web servers to reduce the load on them are two very popular reasons that Azure BLOB storage is used.  If your company is using Azure’s Platform as a Service (PaaS), also known as Cloud Services, interest in BLOB might be elevated with regards to storage because it provides persistent data storage. With Cloud Services you get dedicated virtual machines that run code without having to worry about managing those virtual machines. Unlike the hard drives found in Windows Azure Virtual Machines (the Infrastructure as a Service –IaaS- offering from Microsoft), the hard drives used in Cloud Services instances are not persistent. Because of this, any files you want to have around long term should be put into a persistent store, and this is where BLOB storage is so useful.

BLOB Storage, Windows Azure Tables and Windows Azure Queues make up the Windows Azure Storage services. Azure tables are a non-relational, key-value-pair storage mechanism and the Queue service provides basic message-queuing capabilities. All three of these services store their data within a Windows Azure Storage Account which are required to get started.  Each account can hold up to 200 TB of data in any combination of Tables, Queues or BLOBs and all three can be accessed via public HTTP or HTTPS REST based endpoints, or through a variety of client libraries that wrap the REST interface.

To get started using the BLOB service, a Windows Azure account is required and within Azure, the creation of a Storage Account.  If you have an MSDN Subscription, you can sign up for your Windows Azure benefits to test and dive deeper into the examples listed.

Any file type can be stored in the Windows Azure BLOB Storage service. Image files, database files, text files, or virtual hard drive files can all be stored. It is important to note however, that when they are uploaded to the service Files are stored as either a Page BLOB or a Block BLOB depending on how the file will be utilized or the size of the file being stored.

Page BLOBs are optimized for random reads and writes so they are used frequently when storing virtual hard drive files for virtual machines. It’s no coincidence that, the Page BLOB was introduced when the first virtual drive for Windows Azure was announced. Windows Azure Cloud Drives were initially called Windows Azure X-Drives. Persisted disks used by Microsoft’s IaaS offeringWindows , commonly referred to as Azure Virtual Machines  also use the Page BLOB to store their data and Operating System drives. Each Page BLOB is made up of one or more 512-byte pages of data, up to a total size limit of 1 TB per file.

The majority of files that you upload would benefit from being stored as Block BLOBs, which are written to the storage account as a series of blocks and then committed into a single file.  Create a large file by breaking it into blocks, which can be uploaded concurrently and then then committed together into a single file in one operation. This provides faster upload times and improved throughput. The client storage libraries manage this process by uploading files of less than 64 MB in size in a single operation, and uploading larger files across multiple operations by breaking down the files and running the concurrent uploads. A Block BLOB has a maximum size of 200 GB.

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