Append Blob In Azure

An append blob is a new type of blob, introduced with version 5.x of the Azure storage client library for .NET. An append blob is optimized for append operations, such as logging. Like a block blob, an append blob is comprised of blocks, but when you add a new block to an append blob, it is always appended to the end of the blob. You cannot update or delete an existing block in an append blob. The block IDs for an append blob are not exposed as they are for a block blob.

Each block in an append blob can be a different size, up to a maximum of 4 MB, and an append blob can include a maximum of 50,000 blocks. The maximum size of an append blob is therefore slightly more than 195 GB (4 MB X 50,000 blocks).

The example below creates a new append blob and appends some data to it, simulating a simple logging operation.

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//Parse the connection string for the storage account.
CloudStorageAccount storageAccount = CloudStorageAccount.Parse(
    Microsoft.Azure.CloudConfigurationManager.GetSetting("StorageConnectionString"));

//Create service client for credentialed access to the Blob service.
CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();

//Get a reference to a container.
CloudBlobContainer container = blobClient.GetContainerReference("my-append-blobs");

//Create the container if it does not already exist. 
container.CreateIfNotExists();

//Get a reference to an append blob.
CloudAppendBlob appendBlob = container.GetAppendBlobReference("append-blob.log");

//Create the append blob. Note that if the blob already exists, the CreateOrReplace() method will overwrite it.
//You can check whether the blob exists to avoid overwriting it by using CloudAppendBlob.Exists().
appendBlob.CreateOrReplace();

int numBlocks = 10;

//Generate an array of random bytes.
Random rnd = new Random();
byte[] bytes = new byte[numBlocks];
rnd.NextBytes(bytes);

//Simulate a logging operation by writing text data and byte data to the end of the append blob.
for (int i = 0; i < numBlocks; i++)
{
    appendBlob.AppendText(String.Format("Timestamp: {0} \tLog Entry: {1}{2}",
        DateTime.Now.ToUniversalTime().ToString(), bytes[i], Environment.NewLine));
}

//Read the append blob to the console window.
Console.WriteLine(appendBlob.DownloadText());