Put Block

Article
11/07/2023

The Put Block operation creates a new block to be committed as part of a blob.

Request

You can construct the Put Block request as follows. We recommend that you use HTTPS. Replace myaccount with the name of your storage account:

PUT method request URI	HTTP version
`https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=block&blockid=id`	HTTP/1.1

Emulated storage service request

When you're making a request against the emulated storage service, specify the emulator hostname and Blob service port as 127.0.0.1:10000, followed by the emulated storage account name:

PUT method request URI	HTTP version
`http://127.0.0.1:10000/devstoreaccount1/mycontainer/myblob?comp=block&blockid=id`	HTTP/1.1

For more information, see Use the Azurite emulator for local Azure Storage development.

URI parameters

Parameter	Description
`blockid`	Required. A valid Base64 string value that identifies the block. Before it's encoded, the string must be less than or equal to 64 bytes in size. For a specified blob, the length of the value for the `blockid` parameter must be the same size for each block. Note: The Base64 string must be URL-encoded.
`timeout`	Optional. The `timeout` parameter is expressed in seconds. For more information, see Set time-outs for Blob service operations.

Request headers

The required and optional request headers are described in the following table:

Request header	Description
`Authorization`	Required. Specifies the authorization scheme, account name, and signature. See Authorize requests to Azure Storage for more information.
`Date` or `x-ms-date`	Required. Specifies the Coordinated Universal Time (UTC) for the request. For more information, see Authorize requests to Azure Storage.
`x-ms-version`	Required for all authorized requests. Specifies the version of the operation to use for this request. For more information, see Versioning for the Azure Storage Services.
`Content-Length`	Required. The length of the block content in bytes. The block must be less than or equal to 4,000 mebibytes (MiB) in size for version 2019-12-12 and later. See the Remarks section for limits in older versions. When the length isn't provided, the operation fails with the status code 411 (Length Required).
`Content-MD5`	Optional. An MD5 hash of the block content. This hash is used to verify the integrity of the block during transport. When this header is specified, the storage service compares the hash of the content that has arrived with this header value. Note: This MD5 hash isn't stored with the blob. If the two hashes do not match, the operation fails with error code 400 (Bad Request).
`x-ms-content-crc64`	Optional. A CRC64 hash of the block content. This hash is used to verify the integrity of the block during transport. When this header is specified, the storage service compares the hash of the content that has arrived with this header value. Note: This CRC64 hash isn't stored with the blob. If the two hashes don't match, the operation fails with error code 400 (Bad Request). If both Content-MD5 and x-ms-content-crc64 headers are present, the request fails with a 400 (Bad Request). This header is supported in versions 2019-02-02 and later.
`x-ms-encryption-scope`	Optional. Indicates the encryption scope to use to encrypt the request contents. This header is supported in versions 2019-02-02 and later.
`x-ms-lease-id:<ID>`	Required if the blob has an active lease. To perform this operation on a blob with an active lease, specify the valid lease ID for this header.
`x-ms-client-request-id`	Optional. Provides a client-generated, opaque value with a 1-kibibyte (KiB) character limit that's recorded in the logs when logging is configured. We highly recommend that you use this header to correlate client-side activities with requests that the server receives. For more information, see Monitor Azure Blob Storage.

Request headers (customer-provided encryption keys)

As of version 2019-02-02, the following headers may be specified on the request to encrypt a blob with a customer-provided key. Encryption with a customer-provided key (and the corresponding set of headers) is optional.

Request header	Description
`x-ms-encryption-key`	Required. The Base64-encoded AES-256 encryption key.
`x-ms-encryption-key-sha256`	Required. The Base64-encoded SHA256 hash of the encryption key.
`x-ms-encryption-algorithm: AES256`	Required. Specifies the algorithm to use for encryption. The value of this header must be `AES256`.

Request body

The request body contains the content of the block.

Sample request

Request Syntax:  
PUT https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=block&blockid=AAAAAA%3D%3D HTTP/1.1  
  
Request Headers:  
x-ms-version: 2011-08-18  
x-ms-date: Sun, 25 Sep 2011 14:37:35 GMT  
Authorization: SharedKey myaccount:J4ma1VuFnlJ7yfk/Gu1GxzbfdJloYmBPWlfhZ/xn7GI=  
Content-Length: 1048576

Response

The response includes an HTTP status code and a set of response headers.

Status code

A successful operation returns status code 201 (Created).

For information about status codes, see Status and Error Codes.

Response headers

The response for this operation includes the following headers. The response may also include additional standard HTTP headers. All standard headers conform to the HTTP/1.1 protocol specification.

Response header	Description
`Content-MD5`	Returned so that the client can check for message content integrity. The value of this header is computed by Blob Storage, and it isn't necessarily the same value that's specified in the request headers. For versions 2019-02-02 and later, this header is returned only when the request has this header.
`x-ms-content-crc64`	For versions 2019-02-02 and later, this header is returned so that the client can check for message content integrity. The value of this header is computed by Blob Storage, and it isn't necessarily the same value that's specified in the request headers. This header is returned when `Content-md5` header isn't present in the request.
`x-ms-request-id`	Uniquely identifies the request that was made, and you can use it to troubleshoot the request. For more information, see Troubleshoot API operations.
`x-ms-version`	Indicates the Blob Storage version that was used to execute the request. This header is returned for requests that were made against version 2009-09-19 or later.
`Date`	A UTC date/time value that's generated by the service, which indicates when the response was initiated.
`x-ms-request-server-encrypted: true/false`	Version 2015-12-11 and later. The value of this header is set to `true` if the contents of the request are successfully encrypted by using the specified algorithm. Otherwise, the value is set to `false`.
`x-ms-encryption-key-sha256`	Version 2019-02-02 and later. This header is returned if the request used a customer-provided key for encryption, so that the client can ensure that the contents of the request are successfully encrypted by using the provided key.
`x-ms-encryption-scope`	Version 2019-02-02 and later. This header is returned if the request used an encryption scope, so that the client can ensure that the contents of the request are successfully encrypted by using the encryption scope.
`x-ms-client-request-id`	Can be used to troubleshoot requests and their corresponding responses. The value of this header is equal to the value of the `x-ms-client-request-id` header if it's present in the request and the value contains no more than 1,024 visible ASCII characters. If the `x-ms-client-request-id` header isn't present in the request, it isn't present in the response.

Sample response

Response Status:  
HTTP/1.1 201 Created  
  
Response Headers:  
Transfer-Encoding: chunked  
x-ms-content-crc64: 77uWZTolTHU  
Date: Sun, 25 Sep 2011 23:47:09 GMT  
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0

Authorization

Authorization is required when calling any data access operation in Azure Storage. You can authorize the Put Block operation as described below.

Important

Microsoft recommends using Microsoft Entra ID with managed identities to authorize requests to Azure Storage. Microsoft Entra ID provides superior security and ease of use compared to Shared Key authorization.

Azure Storage supports using Microsoft Entra ID to authorize requests to blob data. With Microsoft Entra ID, you can use Azure role-based access control (Azure RBAC) to grant permissions to a security principal. The security principal may be a user, group, application service principal, or Azure managed identity. The security principal is authenticated by Microsoft Entra ID to return an OAuth 2.0 token. The token can then be used to authorize a request against the Blob service.

To learn more about authorization using Microsoft Entra ID, see Authorize access to blobs using Microsoft Entra ID.

Permissions

Listed below are the RBAC action necessary for a Microsoft Entra user, group, managed identity, or service principal to call the Put Block operation, and the least privileged built-in Azure RBAC role that includes this action:

Azure RBAC action: Microsoft.Storage/storageAccounts/blobServices/containers/blobs/write
Least privileged built-in role: Storage Blob Data Contributor

To learn more about assigning roles using Azure RBAC, see Assign an Azure role for access to blob data.

A shared access signature (SAS) provides secure delegated access to resources in a storage account. With a SAS, you have granular control over how a client can access data. You can specify what resource the client may access, what permissions they have to those resources, and how long the SAS is valid.

The Put Block operation supports three types of shared access signatures: user delegation SAS, service SAS, and account SAS.

As a security best practice, we recommend that you use Microsoft Entra credentials rather than the storage account key, which can be more easily compromised. If your application design requires shared access signatures, use Microsoft Entra credentials to create a user delegation SAS, when possible.

When Shared Key access is disallowed for the storage account, a service SAS token or an account SAS token will not be permitted on a request to Blob Storage. To learn more, see Understand how disallowing Shared Key affects SAS tokens.

User delegation SAS

A user delegation SAS is secured with Microsoft Entra credentials and also by the permissions specified for the SAS.

Calling the Put Block operation using a SAS token delegated to a container or blob resource requires the Write (w) permission as part of the user delegation SAS token.

To learn more about the user delegation SAS, see Create a user delegation SAS.

Service SAS

A service SAS is secured with the storage account key. A service SAS delegates access to a resource in a single Azure Storage service, such as blob storage.

Calling the Put Block operation using a SAS token delegated to a container or blob resource requires the Write (w) permission as part of the service SAS token.

To learn more about the service SAS, see Create a service SAS.

Account SAS

An account SAS is secured with the storage account key. An account SAS delegates access to resources in one or more of the storage services. All of the operations available via a service or user delegation SAS are also available via an account SAS.

The following table indicates the signed resource type and signed permissions to specify when delegating access:

Operation	Signed service	Signed resource type	Signed permission
Put Block	Blob (b)	Object (o)	Write (w)

To learn more about the account SAS, see Create an account SAS.

Remarks

Put Block uploads a block for future inclusion in a block blob. Each block in a block blob can be a different size. A block blob can include a maximum of 50,000 committed blocks.

The following table describes the maximum permitted block and blob sizes, by service version:

Service version	Maximum block size (via `Put Block`)	Maximum blob size (via `Put Block List`)	Maximum blob size via single write operation (via `Put Blob`)
Version 2019-12-12 and later	4,000 MiB	Approximately 190.7 tebibytes (TiB) (4,000 MiB × 50,000 blocks)	5,000 MiB
Versions 2016-05-31 through 2019-07-07	100 MiB	Approximately 4.75 TiB (100 MiB × 50,000 blocks)	256 MiB
Versions earlier than 2016-05-31	4 MiB	Approximately 195 gibibytes (GiB) (4 MiB × 50,000 blocks)	64 MiB

The maximum number of uncommitted blocks that may be associated with a blob is 100,000. If this number is exceeded, the service returns status code 409 (RequestEntityTooLargeBlockCountExceedsLimit).

After you've uploaded a set of blocks, you can create or update the blob on the server from this set by calling the Put Block List operation. Each block in the set is identified by a block ID that's unique within that blob. Block IDs are scoped to a particular blob, so different blobs can have blocks with the same IDs.

If you call Put Block on a blob that doesn't yet exist, a new block blob is created with a content length of 0. This blob is enumerated by the List Blobs operation if the include=uncommittedblobs option is specified. The block or blocks that you upload are not committed until you call Put Block List on the new blob. A blob that's created this way is maintained on the server for a week. If you haven't added more blocks or committed blocks to the blob within that time period, the blob is garbage collected.

A block that has been successfully uploaded with the Put Block operation doesn't become part of a blob until it's committed with Put Block List. Before Put Block List is called to commit the new or updated blob, any calls to Get Blob return the blob contents without the inclusion of the uncommitted block.

If you upload a block that has the same block ID as another block that hasn't yet been committed, the last uploaded block with that ID will be committed on the next successful Put Block List operation.

After Put Block List is called, all uncommitted blocks that are specified in the block list are committed as part of the new blob. Any uncommitted blocks that weren't specified in the block list for the blob are garbage collected and removed from Blob Storage. Any uncommitted blocks are also garbage collected if there are no successful calls to Put Block or Put Block List on the same blob within a week following the last successful Put Block operation. If Put Blob is called on the blob, any uncommitted blocks are garbage collected.

If the blob has an active lease, the client must specify a valid lease ID on the request to write a block to the blob. If the client either doesn't specify a lease ID or specifies an invalid lease ID, Blob Storage returns status code 412 (Precondition Failed). If the client specifies a lease ID but the blob doesn't have an active lease, Blob Storage also returns status code 412 (Precondition Failed).

For a specified blob, all block IDs must be the same length. If a block is uploaded with a block ID of a different length than the block IDs for any existing uncommitted blocks, the service returns error response code 400 (Bad Request).

If you attempt to upload a block that's larger than 4,000 MiB for version 2019-12-12 or later, larger than 100 MiB for version 2016-05-31 or later, or larger than 4 MiB for older versions, the service returns status code 413 (Request Entity Too Large). The service also returns additional information about the error in the response, including the maximum permitted block size, in bytes.

Calling Put Block doesn't update the last modified time of an existing blob.

Calling Put Block on a page blob returns an error.

Calling Put Block on an archived blob returns an error, and calling it on a hot or cool blob doesn't change the blob tier.

Billing

Pricing requests can originate from clients that use Blob Storage APIs, either directly through the Blob Storage REST API, or from an Azure Storage client library. These requests accrue charges per transaction. The type of transaction affects how the account is charged. For example, read transactions accrue to a different billing category than write transactions. The following table shows the billing category for Put Block requests based on the storage account type:

Operation	Storage account type	Billing category
Put Block	Premium block blob Standard general-purpose v2 Standard general-purpose v1	Write operations¹

¹ Put Block operations write blocks to temporary storage using the storage account's default access tier. For example, if you're uploading a blob to the archive tier, any Put Block operations that are part of the upload are charged as write operations based on the storage account's default access tier, not the destination tier. Put Block List and Put Blob operations, however, are charged as write operations based on the destination tier of the blob.

To learn about pricing for the specified billing category, see Azure Blob Storage Pricing.

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