Windows Azure Introduction - Storage: Blob

Starting from today, I will spend some time to introduce Microsoft cloud computing platform - Windows Azure. I will be focuing on the development part on Windows Azure. At the end of this series, we will put some time on how to develop a Windows Azure application with a pretty good example. Moreover, for what Windows Azure is all about, we will not discuss in any details. Please go Bing it and see what you get from there. :-)

Binary large objects—blobs—are often just what an application needs. Whether they hold video, audio, archived email messages, or anything else, they let applications store and access data in a very general way. To use blobs, a developer first creates one or more containers in some storage account. Each of these containers can then hold one or more blobs.

To identify a particular blob, an application supplies a URI of the form:

http://<StorageAccount>.blob.core.windows.net/<Container>/<BlobName>

<StorageAccount> is a unique identifier assigned when a new storage account is created, while <Container> and <BlobName> are the names of a specific container and a blob within that container. Containers can’t be nested—they can contain only blobs, not other containers—so it’s not possible to create a hierarchy of blobs. Still, it’s legal for a blob name to contain a “/”, so a developer can create the illusion of a hierarchy if desired.

Note that blobs can be large—up to 50 gigabytes—and so to make transferring them more efficient, each blob can be subdivided into blocks. If a failure occurs, retransmission can resume with the most recent block rather than sending the entire blob again. Once all of a blob’s blocks have been uploaded, the entire blob can be committed at once.

Containers can be marked as private or public. For blobs in a private container, both read and write requests must be signed using the key for the blob’s storage account. For blobs in a public container, only write requests must be signed; any application is allowed to read the blob. This can be useful in situations such as making video, photos, or other unstructured data generally available on the Internet.