Raise your hand if you’re storing BLOBs in the database.
I get to say that a lot during our training. Every time I say it, nearly every hand in the room goes up. Some hands go up faster than others, but eventually nearly every hand is up.
It’s a design that happens far more often than it should, but it does happen.
Why Store BLOBs in the Database?
People put binary data in the database because they need the data to be point in time consistent with the rest of the database. It’s not enough to save space in the database if you can’t recover the file to a moment in time.
Think about this scenario:
If the contract is being stored inside the database, we can recover to any point in time and have the appropriate version of the document. It may not be the most current version of the contract, but it’s the version of the document that’s consistent with the rest of the database.
Why Not Use the Filesystem?
File systems are great. They do an excellent job of storing files and organizing them into folders. File systems don’t do a great job of being point in time consistent with a relational database. There’s no transaction log to help us roll back writes that are in flight.
It’s a lot of work to get a full database backup and a file system back up to be remotely close to the same point in time. Restoring a database to a point in time is easy. Restoring a file system to a point in time is close to impossible.
Why Not Use an Appliance?
There’s a third option available – some kind of appliance that sits between database and the file system. The appliance should manage file metadata and provide all access to the files in the file system.
Commercial databases ship with features that sound similar. SQL Server has a
FILESTREAM data type and Oracle has both a BFILE and ORD data type. Both of these types let the database interact with files in the file system. But they still have a problem – you’re stuck managing data through the database. Let’s be clear: this is not an appliance.
Content Addressable Storage (CAS) is a mature technology. The idea behind CAS is that a hardware device handles the meta-data for a given incarnation of a file. A developer sends a file into the CAS appliance and the CAS appliance returns a pointer to the file. Whenever the file changes, a new copy is created and a new handle is returned to the developer. Files can’t be modified, so any thing stored in the database can only point to the right version of the file.
We can combine this with a database pretty easily. Instead of storing a file path in the database, we store the handle that we get back from the CAS system.
How Does CAS Solve the Problem?
The main reason people store BLOBs in the database is so they can get blobs that are consistent with a point in time in the database. By using a storage device that cannot be modified (the CAS), we can make sure that the location we’ve stored in the database is always the right location – there’s no way to tamper with the files that we’re storing, so whatever gets stored in the database is correct.
There’s overhead to this approach – old data may never get cleared out. Typically, though, CAS systems store data on large, slow disks. There’s little need for the throughput that we use for a relational database store system. Do those cat pictures really need to be stored on RAID 10 SSDs? Moving BLOB storage outside of the relational database will free up resources for serving queries. Picking the right way to store your BLOB data will make it easier to scale your system.
Kendra says: Finding the right storage for large objects is a huge architectural decision that impacts performance and availability. Choose wisely!
Brent says: Want your SQL Server’s DBCCs and backups to run faster? This can help a lot.
Doug says: “It’s a lot of work to get a full database backup and a file system back up to be remotely close to the same point in time.” -> This is a major drawback that’s easily overlooked. Make sure everyone’s okay with that possibility when choosing the file system for BLOB data.
[!div title1='Select the version of Data Factory service you are using:']
This article outlines how to copy data to and from Azure Blob storage. To learn about Azure Data Factory, read the introductory article.
[!INCLUDE updated-for-az]
Supported capabilitiesMysql Uncompress Gzip
This Azure Blob connector is supported for the following activities:
Specifically, this Blob storage connector supports:
[!NOTE]If you enable the 'Allow trusted Microsoft services to access this storage account' option on Azure Storage firewall settings, using Azure Integration Runtime to connect to Blob storage will fail with a forbidden error, as ADF is not treated as a trusted Microsoft service. Please connect via a Self-hosted Integration Runtime instead.
Get started
[!INCLUDE>PropertyDescriptionRequiredtypeThe type property must be set to AzureBlobStorage (suggested) or AzureStorage (see notes below).YesconnectionStringSpecify the information needed to connect to Storage for the connectionString property.
Mark this field as a SecureString to store it securely in Data Factory. You can also put account key in Azure Key Vault and pull the accountKey configuration out of the connection string. Refer to the following samples and Store credentials in Azure Key Vault article with more details.YesconnectViaThe integration runtime to be used to connect to the data store. You can use Azure Integration Runtime or Self-hosted Integration Runtime (if your data store is in a private network). If not specified, it uses the default Azure Integration Runtime.No
[!NOTE]If you were using 'AzureStorage' type linked service, it is still supported as-is, while you are suggested to use this new 'AzureBlobStorage' linked service type going forward.
Example:
Example: store account key in Azure Key Vault
Shared access signature authentication
A shared access signature provides delegated access to resources in your storage account. You can use a shared access signature to grant a client limited permissions to objects in your storage account for a specified time. You don't have to share your account access keys. The shared access signature is a URI that encompasses in its query parameters all the information necessary for authenticated access to a storage resource. To access storage resources with the shared access signature, the client only needs to pass in the shared access signature to the appropriate constructor or method. For more information about shared access signatures, see Shared access signatures: Understand the shared access signature model.
[!NOTE]
[!TIP]To generate a service shared access signature for your storage account, you can execute the following PowerShell commands. Replace the placeholders and grant the needed permission.
$context = New-AzStorageContext -StorageAccountName <accountName> -StorageAccountKey <accountKey> New-AzStorageContainerSASToken -Name <containerName> -Context $context -Permission rwdl -StartTime <startTime> -ExpiryTime <endTime> -FullUri
To use shared access signature authentication, the following properties are supported:
[!NOTE]If you were using 'AzureStorage' type linked service, it is still supported as-is, while you are suggested to use this new 'AzureBlobStorage' linked service type going forward.
Example:
If you are confused about any instruction, stop and ask. I will not knowingly suggest your any course that might damage your system but sometimes Malware infections are so severe that only option we have is to re-format and re-install the operating system. Avast rootkit scan on startup. Do not keep on going. Back up your data.
Example: store account key in Azure Key Vault
When you create a shared access signature URI, consider the following points:
Service principal authentication
For Azure Storage service principal authentication in general, refer to Authenticate access to Azure Storage using Azure Active Directory.
Conan exiles best armor for cold. To use service principal authentication, follow these steps:
These properties are supported for an Azure Blob storage linked service:
[!NOTE]Service principal authentication is only supported by 'AzureBlobStorage' type linked service but not previous 'AzureStorage' type linked service.
Example:
Managed identities for Azure resources authentication
A data factory can be associated with a managed identity for Azure resources, which represents this specific data factory. You can directly use this managed identity for Blob storage authentication similar to using your own service principal. It allows this designated factory to access and copy data from/to your Blob storage.
Refer to Authenticate access to Azure Storage using Azure Active Directory for Azure Storage authentication in general. To use managed identities for Azure resources authentication, follow these steps:
[!IMPORTANT]If you use PolyBase to load data from Blob (as source or as staging) into SQL Data Warehouse, when using managed identity authentication for Blob, make sure you also follow steps 1 and 2 in this guidance to 1) register your SQL Database server with Azure Active Directory (Azure AD) and 2) assign the Storage Blob Data Contributor role to your SQL Database server; the rest are handled by Data Factory. If your Blob storage is configured with an Azure Virtual Network endpoint, to use PolyBase to load data from it, you must use managed identity authentication as required by PolyBase.
These properties are supported for an Azure Blob storage linked service:
[!NOTE]Managed identities for Azure resources authentication is only supported by 'AzureBlobStorage' type linked service but not previous 'AzureStorage' type linked service.
Example:
Dataset properties
For a full list of sections and properties available for defining datasets, see the Datasets article.
Parquet and delimited text format dataset
To copy data to and from Blob storage in Parquet or delimited text format, refer to Parquet format and Delimited text format article on format-based dataset and supported settings. The following properties are supported for Azure Blob under
location settings in format-based dataset:
[!NOTE]
AzureBlob type dataset with Parquet/Text format mentioned in next section is still supported as-is for Copy/Lookup/GetMetadata activity for backward compatibility, but it doesn't work with Mapping Data Flow. You are suggested to use this new model going forward, and the ADF authoring UI has switched to generating these new types.
Example:
Other format dataset
To copy data to and from Blob storage in ORC/Avro/JSON/Binary format, set the type property of the dataset to AzureBlob. The following properties are supported.
[!TIP]To copy all blobs under a folder, specify folderPath only.
To copy a single blob with a given name, specify folderPath with folder part and fileName with file name. To copy a subset of blobs under a folder, specify folderPath with folder part and fileName with wildcard filter.
Example:
Copy activity properties
For a full list of sections and properties available for defining activities, see the Pipelines article. This section provides a list of properties supported by the Blob storage source and sink.
Blob storage as a source type
Parquet and delimited text format source
To copy data from Blob storage in Parquet or delimited text format, refer to Parquet format and Delimited text format article on format-based copy activity source and supported settings. The following properties are supported for Azure Blob under
storeSettings settings in format-based copy source:
[!NOTE]For Parquet/delimited text format, BlobSource type copy activity source mentioned in next section is still supported as-is for backward compatibility. You are suggested to use this new model going forward, and the ADF authoring UI has switched to generating these new types.
Example:
Other format source
To copy data from Blob storage in ORC/Avro/JSON/Binary format, set the source type in the copy activity to BlobSource. The following properties are supported in the copy activity source section.
Example:
Blob storage as a sink type
Parquet and delimited text format sink
To copy data to Blob storage in Parquet or delimited text format, refer to Parquet format and Delimited text format article on format-based copy activity sink and supported settings. The following properties are supported for Azure Blob under
storeSettings settings in format-based copy sink:
[!NOTE]For Parquet/delimited text format, BlobSink type copy activity sink mentioned in next section is still supported as-is for backward compatibility. You are suggested to use this new model going forward, and the ADF authoring UI has switched to generating these new types.
Example:
Other format sink
To copy data to Blob storage, set the sink type in the copy activity to BlobSink. The following properties are supported in the sink section.
Example:
Folder and file filter examples
This section describes the resulting behavior of the folder path and file name with wildcard filters.
Some recursive and copyBehavior examples
This section describes the resulting behavior of the Copy operation for different combinations of recursive and copyBehavior values.
Mapping Data Flow properties
Learn details from source transformation and sink transformation in Mapping Data Flow.
Next steps
For a list of data stores supported as sources and sinks by the copy activity in Data Factory, see Supported data stores.
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