Why upload to Azure blob so slow?

Question

I have a custom stream that is used to perform write operations directly into the page cloud blob.

public sealed class WindowsAzureCloudPageBlobStream : Stream
{
    // 4 MB is the top most limit for page blob write operations
    public const int MaxPageWriteCapacity = 4 * 1024 * 1024;

    // Every operation on a page blob has to manipulate a value which is rounded up to 512 bytes
    private const int PageBlobPageAdjustmentSize = 512;

    private CloudPageBlob _pageBlob;

    public override void Write(byte[] buffer, int offset, int count)
    {
        var additionalOffset = 0;
        var bytesToWriteTotal = count;

        List<Task> list = new List<Task>();
        while (bytesToWriteTotal > 0)
        {
            var bytesToWriteTotalAdjusted = RoundUpToPageBlobSize(bytesToWriteTotal);

            // Azure does not allow us to write as many bytes as we want
            // Max allowed size per write is 4MB
            var bytesToWriteNow = Math.Min((int)bytesToWriteTotalAdjusted, MaxPageWriteCapacity);
            var adjustmentBuffer = new byte[bytesToWriteNow];
            ...
            var memoryStream = new MemoryStream(adjustmentBuffer, 0, bytesToWriteNow, false, false);
            var task = _pageBlob.WritePagesAsync(memoryStream, Position, null);
            list.Add(task);
        }

        Task.WaitAll(list.ToArray());
    }

    private static long RoundUpToPageBlobSize(long size) 
    { 
        return (size + PageBlobPageAdjustmentSize - 1) & ~(PageBlobPageAdjustmentSize - 1); 
    }

I have a low performance of Write(). For example:

Stopwatch s = new Stopwatch();
s.Start();
using (var memoryStream = new MemoryStream(adjustmentBuffer, 0, bytesToWriteNow, false, false))
{
      _pageBlob.WritePages(memoryStream, Position);
}

s.Stop();
Console.WriteLine(s.Elapsed); => 00:00:01.52 == Average speed 2.4 MB/s

How can I improve my algorithm? How to use Parallel.ForEach to speedup the process?

Why just only 2.5 MB/sec, but not a 60MB/sec as in official site or http://blogs.microsoft.co.il/applisec/2012/01/05/windows-azure-benchmarks-part-2-blob-write-throughput/

Answer 1

One simple and quick thing to check: make sure your blob storage is in the same Azure region where your VM or Application is running. One issue that we ran into was our storage account was in another region from our application. This caused us a significant delay during processing. We were scratching our heads until we realized we were reading and writing across regions. Rookie mistake on our part!