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Transfer data with the Data Movement library

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The Azure Storage Data Movement library is a cross-platform open source library that is designed for high performance uploading, downloading, and copying of blobs and files. The Data Movement library provides convenient methods that aren't available in the Azure Storage client library for .NET. These methods allow you to set the number of parallel operations, track transfer progress, resume a canceled transfer, and more.

The Data Movement library is only available for .NET, and only supports Azure Blob Storage and Azure Files. You should consider these limitations and other known issues when deciding whether to use the Data Movement library.

If you're migrating code from the older Microsoft.Azure.Storage.DataMovement library (version 2.X.X) to the current Azure.Storage.DataMovement library (version 12.X.X), see the Migration guide.

API reference docs | Source code | Package (NuGet) | Samples: Blobs / Files.Shares

Prerequisites

Set up your environment

If you don't have an existing project, this section shows you how to set up a project to work with the Azure Blob Storage client library for .NET. The steps include package installation, adding using directives, and creating an authorized client object.

Install packages

From your project directory, install packages for the Azure Storage Data Movement client library and the Azure Identity client library using the dotnet add package command. The Azure.Identity package is needed for passwordless connections to Azure services.

dotnet add package Azure.Storage.DataMovement
dotnet add package Azure.Storage.DataMovement.Blobs
dotnet add package Azure.Identity

To work with extension library for Azure Files, install the Azure.Storage.DataMovement.Files.Shares package:

dotnet add package Azure.Storage.DataMovement.Files.Shares

Add using directives

To run the code examples in this article, add the following using directives:

using Azure;
using Azure.Core;
using Azure.Identity;
using Azure.Storage.DataMovement;
using Azure.Storage.DataMovement.Blobs;

If you're using the extension library for Azure Files, add the following using directive:

using Azure.Storage.DataMovement.Files.Shares;

Authorization

The authorization mechanism must have the necessary permissions to perform upload, download, or copy operations. For authorization with Microsoft Entra ID (recommended), you need Azure RBAC built-in role Storage Blob Data Contributor or higher.

About the Data Movement library

The Azure Storage Data Movement library consists of a common client library, and extension libraries for Azure Blob Storage and Azure Files. The common library provides the core functionality for transferring data, while the extension libraries provide functionality specific to Blob Storage and Azure Files. To learn more, see the following resources:

Create a TransferManager object

TransferManager is the main class for starting and controlling all types of transfers, including upload, download, and copy. In this section, you learn how to create a TransferManager object to work with a local file system, Blob Storage, or Azure Files.

Note

A best practice for Azure SDK client management is to treat a client as a singleton, meaning that a class only has one object at a time. There's no need to keep more than one instance of a client for a given set of constructor parameters or client options.

The following code shows how to create a TransferManager object:

TransferManager transferManager = new(new TransferManagerOptions());

You can optionally provide an instance of TransferManagerOptions to the constructor, which applies certain configuration options to all transfers started by the TransferManager object. The following configuration options are available:

  • CheckpointStoreOptions: Optional. Defines the options for creating a checkpoint used for saving transfer state so transfers can be resumed.
  • Diagnostics: Gets the transfer manager diagnostic options.
  • ErrorHandling: Optional. Defines how errors are handled during a transfer. Default is StopOnAnyFailure.
  • MaximumConcurrency: The maximum number of workers that can be used in a parallel transfer.
  • ProvidersForResuming: Resource providers for the transfer manager to use in resuming a transfer. Expects one provider for each storage provider in use. To learn more, see Resume an existing transfer.

Create a StorageResource object

StorageResource is the base class for all storage resources, including blobs and files. To create a StorageResource object, use one of the following provider classes:

Create a StorageResource object for Blob Storage

The following code shows how to create a StorageResource object for blob containers and blobs using a Uri:

// Create a token credential
TokenCredential tokenCredential = new DefaultAzureCredential();

BlobsStorageResourceProvider blobsProvider = new(tokenCredential);

// Get a container resource
StorageResource container = await blobsProvider.FromContainerAsync(
    new Uri("http://<storage-account-name>.blob.core.windows.net/sample-container"));

// Get a block blob resource - default is block blob
StorageResource blockBlob = await blobsProvider.FromBlobAsync(
    new Uri("http://<storage-account-name>.blob.core.windows.net/sample-container/sample-block-blob"),
    new BlockBlobStorageResourceOptions());

// Use a similar approach to get a page blob or append blob resource

You can also create a StorageResource object using a client object from Azure.Storage.Blobs.

// Create a token credential
TokenCredential tokenCredential = new DefaultAzureCredential();

BlobContainerClient blobContainerClient = new(
    new Uri("https://<storage-account-name>.blob.core.windows.net/sample-container"),
    tokenCredential);
StorageResource containerResource = BlobsStorageResourceProvider.FromClient(blobContainerClient);

BlockBlobClient blockBlobClient = blobContainerClient.GetBlockBlobClient("sample-block-blob");
StorageResource blockBlobResource = BlobsStorageResourceProvider.FromClient(blockBlobClient);

// Use a similar approach to get a page blob or append blob resource

Start a new transfer

All transfers need to specify a source and a destination. Both the source and destination are type StorageResource, which can be either StorageResourceContainer or StorageResourceItem. For a given transfer, the source and destination must be of the same kind. For example, if the source is a blob container, the destination must be a blob container.

You can start a new transfer by calling the following method:

This method returns a TransferOperation object that represents the transfer. You can use the TransferOperation object to monitor the transfer progress or obtain the transfer ID. The transfer ID is a unique identifier for the transfer that's needed to resume a transfer or pause a transfer.

You can optionally provide an instance of TransferOptions to StartTransferAsync or ResumeTransferAsync, which applies certain configuration options to a specific transfer. The following configuration options are available:

  • CreationMode: Configures the behavior when a transfer encounters a resource that already exists. Defaults to FailIfExists when starting a new transfer. When you resume a transfer, the defaults can vary. For all resources successfully enumerated when the transfer started, CreationMode defaults to the initial value used. For any remaining resources, the regular default value applies.
  • InitialTransferSize: The size of the first range request in bytes. Single transfer sizes smaller than this limit are uploaded or downloaded in a single request. Transfers larger than this limit continue being downloaded or uploaded in chunks of size MaximumTransferChunkSize. The default value is 32 MiB. When you resume a transfer, the default value is the value specified when the transfer first started.
  • MaximumTransferChunkSize: The maximum size to use for each chunk when transferring data in chunks. The default value is 4 MiB. When you resume a transfer, the default value is the value specified when the transfer first started.
  • ProgressHandlerOptions: Optional. Options for changing behavior of the ProgressHandler.

Example: Upload a local directory to a blob container

The following code example shows how to start a new transfer to upload a local directory to a blob container:

// Create a token credential
TokenCredential tokenCredential = new DefaultAzureCredential();

TransferManager transferManager = new(new TransferManagerOptions());

BlobsStorageResourceProvider blobsProvider = new(tokenCredential);

string localDirectoryPath = "C:/path/to/directory";
Uri blobContainerUri = new Uri("https://<storage-account-name>.blob.core.windows.net/sample-container");

TransferOperation transferOperation = await transferManager.StartTransferAsync(
    sourceResource: LocalFilesStorageResourceProvider.FromDirectory(localDirectoryPath),
    destinationResource: await blobsProvider.FromContainerAsync(blobContainerUri));
await transferOperation.WaitForCompletionAsync();

Example: Copy a container or blob

You can use the Data Movement library to copy between two StorageResource instances. For blob resources, the transfer uses the Put Blob From URL operation, which performs a server-to-server copy.

The following code example shows how to start a new transfer to copy all blobs in a source blob container to a destination blob container. The destination container must already exist. In this example, we set CreationMode to OverwriteIfExists to overwrite any destination blobs that already exist. You can adjust the CreationMode property based on the needs of your app.

Uri sourceContainerUri = new Uri("https://<storage-account-name>.blob.core.windows.net/source-container");
Uri destinationContainerUri = new Uri("https://<storage-account-name>.blob.core.windows.net/dest-container");

TransferOperation transferOperation = await transferManager.StartTransferAsync(
    sourceResource: await blobsProvider.FromContainerAsync(
        sourceContainerUri,
        new BlobStorageResourceContainerOptions()
        {
            BlobPrefix = "source/directory/prefix"
        }),
    destinationResource: await blobsProvider.FromContainerAsync(
        destinationContainerUri,
        new BlobStorageResourceContainerOptions()
        {
            // All source blobs are copied as a single type of destination blob
            // Defaults to block blob, if not specified
            BlobType = BlobType.Block,
            BlobPrefix = "destination/directory/prefix"
        }),
    transferOptions: new TransferOptions()
    {
        CreationMode = StorageResourceCreationMode.OverwriteIfExists,
    }
);
await transferOperation.WaitForCompletionAsync();

The following code example shows how to start a new transfer to copy a source blob to a destination blob. In this example, we set CreationMode to OverwriteIfExists to overwrite the destination blob if it already exists. You can adjust the CreationMode property based on the needs of your app.

Uri sourceBlobUri = new Uri(
    "https://<storage-account-name>.blob.core.windows.net/source-container/source-blob");
Uri destinationBlobUri = new Uri(
    "https://<storage-account-name>.blob.core.windows.net/dest-container/dest-blob");

TransferOperation transferOperation = await transferManager.StartTransferAsync(
    sourceResource: await blobsProvider.FromBlobAsync(sourceBlobUri),
    destinationResource: await blobsProvider.FromBlobAsync(destinationBlobUri, new BlockBlobStorageResourceOptions()),
    transferOptions: new TransferOptions()
    {
        CreationMode = StorageResourceCreationMode.OverwriteIfExists,
    }
);
await transferOperation.WaitForCompletionAsync();

Resume an existing transfer

By persisting transfer progress to disk, the Data Movement library allows you to resume a transfer that failed before completion, or was otherwise canceled or paused. To resume a transfer, the TransferManager object must be configured with StorageResourceProvider instances that are capable of reassembling the transfer from the persisted data. You can use the ProvidersForResuming property of the TransferManagerOptions class to specify the providers.

The following code example shows how to initialize a TransferManager object that's capable of resuming a transfer between the local file system and Blob Storage:

// Create a token credential
TokenCredential tokenCredential = new DefaultAzureCredential();

TransferManager transferManager = new(new TransferManagerOptions()
{
    ProvidersForResuming = new List<StorageResourceProvider>()
    {
        new BlobsStorageResourceProvider(tokenCredential)
    }
});

To resume a transfer, call the following method:

Provide the transfer ID of the transfer that you want to resume. The transfer ID is a unique identifier for the transfer that's returned as part of the TransferOperation object when the transfer is started. If you don't know the transfer ID value, you can call TransferManager.GetTransfersAsync to find the transfer and its corresponding ID.

The following code example shows how to resume a transfer:

TransferOperation resumedTransfer = await transferManager.ResumeTransferAsync(transferId: ID);

Note

The location of the persisted transfer data is different than the default location if TransferCheckpointStoreOptions is set as part of TransferManagerOptions. To resume transfers recorded with a custom checkpoint store, you must provide the same checkpoint store options for the TransferManager object that resumes the transfer.

Monitor transfer progress

Transfers can be monitored and observed through several mechanisms, depending on the needs of your app. In this section, you learn how to monitor transfer progress using the TransferOperation object, and how to monitor a transfer using TransferOptions events.

Example: Monitor transfer progress using the TransferOperation object

You can monitor transfer progress using the TransferOperation object returned by the StartTransferAsync method. You can also call TransferManager.GetTransfersAsync to enumerate all transfers for a TransferManager object.

The following code example shows how to iterate over all transfers and write the state of each transfer to a log file:

async Task CheckTransfersAsync(TransferManager transferManager)
{
    await foreach (TransferOperation transfer in transferManager.GetTransfersAsync())
    {
        using StreamWriter logStream = File.AppendText("path/to/log/file");
        logStream.WriteLine(Enum.GetName(typeof(TransferState), transfer.Status.State));
    }
}

TransferStatus defines the status of the transfer job. TransferStatus includes the following properties:

Property Type Description
HasCompletedSuccessfully Boolean Represents if the transfer completes successfully without any failure or skipped items.
HasFailedItems Boolean Represents if transfer has any failure items. If set to true, the transfer has at least one failure item. If set to false, the transfer currently has no failures.
HasSkippedItems Boolean Represents if transfer has any skipped items. If set to true, the transfer has at least one skipped item. If set to false, the transfer currently has no skipped items. It's possible to never have any items skipped if SkipIfExists isn't enabled in TransferOptions.CreationMode.
State TransferState Defines the types of the state a transfer can have. See TransferState for details.

Example: Monitor transfer progress using TransferOptions events

You can monitor transfer progress by listening for events provided by the TransferOptions class. The TransferOptions instance is passed to the StartTransferAsync method and provides events that are triggered when a transfer completes, fails, is skipped, or changes status.

The following code example shows how to listen for a transfer completion event using TransferOptions:

async Task<TransferOperation> ListenToTransfersAsync(
    TransferManager transferManager,
    StorageResource source,
    StorageResource destination)
{
    TransferOptions transferOptions = new();
    transferOptions.ItemTransferCompleted += (TransferItemCompletedEventArgs args) =>
    {
        using (StreamWriter logStream = File.AppendText("path/to/log/file"))
        {
            logStream.WriteLine($"File Completed Transfer: {args.Source.Uri.AbsoluteUri}");
        }
        return Task.CompletedTask;
    };
    return await transferManager.StartTransferAsync(
        source,
        destination,
        transferOptions);
}

Use extension methods for BlobContainerClient

For applications with existing code that uses the BlobContainerClient class from Azure.Storage.Blobs, you can use extension methods to start transfers directly from a BlobContainerClient object. The extension methods are provided in the BlobContainerClientExtensions class (or ShareDirectoryClientExtensions for Azure Files), and provide some of the benefits of using TransferManager with minimal code changes. In this section, you learn how to use the extension methods to perform transfers from a BlobContainerClient object.

Install the Azure.Storage.Blobs package if you don't have it already:

dotnet add package Azure.Storage.Blobs

Add the following using directives to the top of your code file:

using Azure.Storage.Blobs;
using Azure.Storage.Blobs.Models;

The following code example shows how to instantiate a BlobContainerClient for a blob container named sample-container:

// Create a token credential
TokenCredential tokenCredential = new DefaultAzureCredential();

BlobServiceClient client = new BlobServiceClient(
    new Uri("https://<storage-account-name>.blob.core.windows.net"),
    tokenCredential);

BlobContainerClient containerClient = client.GetBlobContainerClient("sample-container");

The following code example shows how to upload local directory contents to sample-container using UploadDirectoryAsync:

TransferOperation transfer = await containerClient
    .UploadDirectoryAsync(WaitUntil.Started, "local/directory/path");

await transfer.WaitForCompletionAsync();

The following code example shows how to download the contents of sample-container to a local directory using DownloadToDirectoryAsync:

TransferOperation transfer = await containerClient
    .DownloadToDirectoryAsync(WaitUntil.Started, "local/directory/path");

await transfer.WaitForCompletionAsync();

To learn more about the extension methods for BlobContainerClient, see Extensions on BlobContainerClient.

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