title: Can PutBlock be used to append to an existing BlockBlob in Azure
body: <p>As per the title, I have a program whereby I'm trying to add to an existing BlobkBlob using the PutBlock method:</p>
  
  <pre><code>    private static void UploadNewText(string text)
      {
          string fileName = "test4.txt";
          string containerString = "mycontainer";
  
          CloudStorageAccount storage = CloudStorageAccount.Parse(connection);
          CloudBlobClient client = storage.CreateCloudBlobClient();
          CloudBlobContainer container = client.GetContainerReference(containerString);
          CloudBlockBlob blob = container.GetBlockBlobReference(fileName);
  
          using (MemoryStream stream = new MemoryStream())
          using (StreamWriter sw = new StreamWriter(stream))
          {
              sw.Write(text);
              sw.Flush();
              stream.Position = 0;
  
              string blockId = Convert.ToBase64String(
                  ASCIIEncoding.ASCII.GetBytes("0000005"));
  
              Console.WriteLine(blockId);
  
              blob.PutBlock(blockId, stream, null);
              blob.PutBlockList(new string[] { blockId });
          }
      }
  </code></pre>
  
  <p>As I understand it, providing the BlockId increases (or at least differs), and is a consistent size, this should work; however, when I run it a second time for the same file (regardless of whether or not I increase the Block ID) it just overwrites the existing file with the new text.</p>
  
  <p>I realise there are other options for appending to a blob (such as AppendBlob), but I'm curious if PutBlock, specifically can do this.  Is what I am trying to do possible and, if so, what am I doing wrong?</p>