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CloudBlockBlob.PutBlockList Method (IEnumerable)

Updated: April 24, 2013


Uploads a list of blocks to a new or existing blob.

Namespace: Microsoft.WindowsAzure.StorageClient
Assembly: Microsoft.WindowsAzure.StorageClient (in Microsoft.WindowsAzure.StorageClient.dll)

Dim instance As CloudBlockBlob
Dim blockList As IEnumerable(Of String)


void PutBlockList (
	IEnumerable<String^>^ blockList



Type: System.Collections.Generic.IEnumerable

An enumerable collection of block IDs, as base64-encoded strings.

The following code example writes a set of blocks to a block blob, then commits the blocks to create or update the blob.

static void BlockBlobUploadManyBlocks(Uri blobEndpoint, string accountName, string accountKey)
    CloudBlobClient blobClient = new CloudBlobClient(blobEndpoint, 
        new StorageCredentialsAccountAndKey(accountName, accountKey));

    //Get a reference to a block blob.
    CloudBlockBlob blob = blobClient.GetBlockBlobReference("mycontainer/myblockblob");

    //Create a list to hold the block list.
    var blockList = new List<string>();

    byte[] data = new byte[100];
        //Write blocks to the blob.
        using (var stream = new System.IO.MemoryStream(data))
            //Create a block ID. All block ID strings must have same length.
            string blockID = Convert.ToBase64String(Encoding.UTF8.GetBytes(x.ToString()));

            blob.PutBlock(blockID, stream, null);

    //Commit the block list of blocks we have uploaded.

The PutBlockList method writes a blob by specifying the list of block IDs that make up the blob. In order to be written as part of a blob, a block must have been successfully written to the service using PutBlock.

By calling PutBlockList, you can modify an existing blob by inserting, updating, or deleting individual blocks, without uploading the whole blob again. You can specify block IDs from both the current committed block list and the uncommitted block list to create a new blob or update the content of an existing blob. In this way you can update a blob by specifying a few new blocks from the uncommitted block list, and the rest from the committed block list, which are already part of the existing blob.

The maximum number of blocks that may be committed is 50,000, and the maximum size of a blob that may be committed via PutBlockList is 200 GB. The maximum number of uncommitted blocks that may be associated with a blob is 100,000, and the maximum size of the uncommitted block list is 400 GB.

When you call PutBlockList to update an existing blob, the blob's existing properties and metadata are overwritten. However, any existing snapshots are retained with the blob. You can use include an access condition to perform the operation only if a specified condition is met.

If PutBlockList fails due to a missing block, you will need to upload the missing block.

Any uncommitted blocks will be garbage collected if there are no successful calls to upload a block or commit the block list within a week following the last successful block upload. If the blob's contents are modified in some other way, any uncommitted blocks will be garbage collected.


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