Blobs are files and are designed to store images, audio, video files, Excel spread sheets, Word documents and virtual hard drives (VHDs). Blob stands for 'binary large object'.
Azure ensures that you can access blob data using URLs so that there is wide flexibility to access the blob data.
A storage account is required to use blob storage service. After creating a storage account, you have to create containers and place the blobs in these containers. A storage account can have any number of containers. There is no restriction on the number of blobs in a container. However, there is a restriction on the capacity of each storage account and it is restricted to 500TB. Which means you can have any number of blob files and containers with in the limit of 500TB.
Remember azure does not allow you to create a container within a container.
There are two types of blobs are available in azure. They are block blobs and page blobs.
This type of blobs are designed to hold files which are smaller in size comparatively. Files such as images have to be read from the beginning to the end completely and then displayed. Block blobs are suitable for storing such files. The name block blob is acquired because small blocks of blobs are assembled to form a blob.
This type of blobs are designed to hold files which are in the range of 1TB. Large movie files are the typical example. These type of data needs to be accessed at any point and read. To meet this requirement, the files are stored as pages and hence the name page blobs.
virtual hard drives (VHDs)
A virtual hard drive is a hard drive format created on a hard disk and simulates the characteristics of a physical hard disk. You can store files and OS on virtual hard drives. This is particularly useful to developers to test their applications on different versions of operating systems.