The Azure Blob service supports the creation of read-only snapshots of a blob. A storage account is billed only for those blocks and pages in a snapshot that differ from those in the underlying blob. A blob snapshot is useful in providing a backup for a blob, as it can be used to reset the blob to an earlier state. Indeed, multiple snapshots can be made over time, allowing a historic record to be kept of the changes made to a blob.

A blob snapshot is created using the CloudBlockBlob.CreateSnapshot() method. Each snapshot of a blob is distinguished by its creation time, which must be provided to operations that are accessing the snapshot. A snapshot created at a particular datetime is addressed by appending a snapshot={datetime} query string to the URL, thus identifying the underlying blob.

For example, the following is the complete URL for a snapshot taken on 11/25/2010 of a blob named SnapshotsExample:

http://myaccountname.blob.core.windows.net/ chapter2...