Uploading Big Files in Windows Azure Blob Storage using PutListBlock

Windows Azure Blob Storage could be analogized as file-system on the cloud. It enables us to store any unstructured data file such as text, images, video, etc. In this post, I will show how to upload big file into Windows Azure Storage. Please be inform that we will be using Block Blob for this case. For more information about Block Blob and Page Block, please visit here.

I am assume that you know how to upload a file to Windows Azure Storage. If you don’t know, I would recommend you to check out this lab from Windows Azure Training Kit.

Uploading a blob (commonly-used technique)

The following snippet show you how to upload a blob using a commonly-used technique, blob.UploadFromStream() which eventually invoking PutBlob REST-API.

protected void btnUpload_Click(object sender, EventArgs e)
{
    var storageAccount = CloudStorageAccount.FromConfigurationSetting("DataConnectionString");
    blobClient = storageAccount.CreateCloudBlobClient();

    CloudBlobContainer container = blobClient.GetContainerReference("image2");
    container.CreateIfNotExist();

    var permission = container.GetPermissions();
    permission.PublicAccess = BlobContainerPublicAccessType.Container;
    container.SetPermissions(permission);

    string name = fu.FileName;
    CloudBlob blob = container.GetBlobReference(name);
    blob.UploadFromStream(fu.FileContent);
}

The above code snippet works well in most case. Although you could upload at maximum 64 MB per file (for block blob), it’s more recommended to upload using another technique which I am going to describe more detail.

Uploading a blob by splitting it into chunks and calling PutBlockList

The idea of this technique is to split a block blob into smaller chunk of blocks, uploading them one-by-one or in-parallel and eventually join them all by calling PutBlockList().

protected void btnUpload_Click(object sender, EventArgs e)
{
    CloudBlobClient blobClient;
    var storageAccount = CloudStorageAccount.FromConfigurationSetting("DataConnectionString");
    blobClient = storageAccount.CreateCloudBlobClient();

    CloudBlobContainer container = blobClient.GetContainerReference("mycontainer");
    container.CreateIfNotExist();

    var permission = container.GetPermissions();
    permission.PublicAccess = BlobContainerPublicAccessType.Container;
    container.SetPermissions(permission);

    string name = fu.FileName;
    CloudBlockBlob blob = container.GetBlockBlobReference(name);

    blob.UploadFromStream(fu.FileContent);

    int maxSize = 1 * 1024 * 1024; // 4 MB

    if (fu.PostedFile.ContentLength > maxSize)
    {
        byte[] data = fu.FileBytes; 
        int id = 0;
        int byteslength = data.Length;
        int bytesread = 0;
        int index = 0;
        List<string> blocklist = new List<string>();
        int numBytesPerChunk = 250 * 1024; //250KB per block
    
        do
        {
            byte[] buffer = new byte[numBytesPerChunk];
            int limit = index + numBytesPerChunk;
            for (int loops = 0; index < limit; index++)
            {
                buffer[loops] = data[index];
                loops++;
            }
            bytesread = index;
            string blockIdBase64 = Convert.ToBase64String(System.BitConverter.GetBytes(id));

            blob.PutBlock(blockIdBase64, new MemoryStream(buffer, true), null); 
            blocklist.Add(blockIdBase64);
            id++;
        } while (byteslength - bytesread > numBytesPerChunk);

        int final = byteslength - bytesread;
        byte[] finalbuffer = new byte[final];
        for (int loops = 0; index < byteslength; index++)
        {
            finalbuffer[loops] = data[index];
            loops++;
        }
        string blockId = Convert.ToBase64String(System.BitConverter.GetBytes(id));
        blob.PutBlock(blockId, new MemoryStream(finalbuffer, true), null);
        blocklist.Add(blockId);

        blob.PutBlockList(blocklist); 
    }
    else
        blob.UploadFromStream(fu.FileContent);            
}

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