Azure SQL Database managed instance T-SQL differences from SQL Server

This article summarizes and explains the differences in syntax and behavior between Azure SQL Database managed instance and on-premises SQL Server Database Engine. The following subjects are discussed:

The managed instance deployment option provides high compatibility with on-premises SQL Server Database Engine. Most of the SQL Server database engine features are supported in a managed instance.

Migration

Availability

Always On

High availability is built into managed instance and can't be controlled by users. The following statements aren't supported:

Backup

Managed instances have automatic backups, so users can create full database COPY_ONLY backups. Differential, log, and file snapshot backups aren't supported.

  • With a managed instance, you can back up an instance database only to an Azure Blob storage account:
    • Only BACKUP TO URL is supported.
    • FILE, TAPE, and backup devices aren't supported.
  • Most of the general WITH options are supported.
    • COPY_ONLY is mandatory.
    • FILE_SNAPSHOT isn't supported.
    • Tape options: REWIND, NOREWIND, UNLOAD, and NOUNLOAD aren't supported.
    • Log-specific options: NORECOVERY, STANDBY, and NO_TRUNCATE aren't supported.

Limitations:

  • With a managed instance, you can back up an instance database to a backup with up to 32 stripes, which is enough for databases up to 4 TB if backup compression is used.

  • You can't execute BACKUP DATABASE ... WITH COPY_ONLY on a database that's encrypted with service-managed Transparent Data Encryption (TDE). Service-managed TDE forces backups to be encrypted with an internal TDE key. The key can't be exported, so you can't restore the backup. Use automatic backups and point-in-time restore, or use customer-managed (BYOK) TDE instead. You also can disable encryption on the database.

  • The maximum backup stripe size by using the BACKUP command in a managed instance is 195 GB, which is the maximum blob size. Increase the number of stripes in the backup command to reduce individual stripe size and stay within this limit.

    Tip

    To work around this limitation, when you back up a database from either SQL Server in an on-premises environment or in a virtual machine, you can:

    • Back up to DISK instead of backing up to URL.
    • Upload the backup files to Blob storage.
    • Restore into the managed instance.

    The Restore command in a managed instance supports bigger blob sizes in the backup files because a different blob type is used for storage of the uploaded backup files.

For information about backups using T-SQL, see BACKUP.

Security

Auditing

The key differences between auditing in databases in Azure SQL Database and databases in SQL Server are:

  • With the managed instance deployment option in Azure SQL Database, auditing works at the server level. The .xel log files are stored in Azure Blob storage.
  • With the single database and elastic pool deployment options in Azure SQL Database, auditing works at the database level.
  • In SQL Server on-premises or virtual machines, auditing works at the server level. Events are stored on file system or Windows event logs.

XEvent auditing in managed instance supports Azure Blob storage targets. File and Windows logs aren't supported.

The key differences in the CREATE AUDIT syntax for auditing to Azure Blob storage are:

  • A new syntax TO URL is provided that you can use to specify the URL of the Azure Blob storage container where the .xel files are placed.
  • The syntax TO FILE isn't supported because a managed instance can't access Windows file shares.

For more information, see:

Certificates

A managed instance can't access file shares and Windows folders, so the following constraints apply:

  • The CREATE FROM/BACKUP TO file isn't supported for certificates.
  • The CREATE/BACKUP certificate from FILE/ASSEMBLY isn't supported. Private key files can't be used.

See CREATE CERTIFICATE and BACKUP CERTIFICATE.

Workaround: Script for the certificate or private key, store as .sql file, and create from binary:

CREATE CERTIFICATE  
   FROM BINARY = asn_encoded_certificate
WITH PRIVATE KEY (<private_key_options>)

Credential

Only Azure Key Vault and SHARED ACCESS SIGNATURE identities are supported. Windows users aren't supported.

See CREATE CREDENTIAL and ALTER CREDENTIAL.

Cryptographic providers

A managed instance can't access files, so cryptographic providers can't be created:

Logins and users

  • SQL logins created by using FROM CERTIFICATE, FROM ASYMMETRIC KEY, and FROM SID are supported. See CREATE LOGIN.

  • Azure Active Directory (Azure AD) server principals (logins) created with the CREATE LOGIN syntax or the CREATE USER FROM LOGIN [Azure AD Login] syntax are supported (public preview). These logins are created at the server level.

    Managed instance supports Azure AD database principals with the syntax CREATE USER [AADUser/AAD group] FROM EXTERNAL PROVIDER. This feature is also known as Azure AD contained database users.

  • Windows logins created with the CREATE LOGIN ... FROM WINDOWS syntax aren't supported. Use Azure Active Directory logins and users.

  • The Azure AD user who created the instance has unrestricted admin privileges.

  • Non-administrator Azure AD database-level users can be created by using the CREATE USER ... FROM EXTERNAL PROVIDER syntax. See CREATE USER ... FROM EXTERNAL PROVIDER.

  • Azure AD server principals (logins) support SQL features within one managed instance only. Features that require cross-instance interaction, no matter whether they're within the same Azure AD tenant or different tenants, aren't supported for Azure AD users. Examples of such features are:

    • SQL transactional replication.
    • Link server.
  • Setting an Azure AD login mapped to an Azure AD group as the database owner isn't supported.

  • Impersonation of Azure AD server-level principals by using other Azure AD principals is supported, such as the EXECUTE AS clause. EXECUTE AS limitations are:

    • EXECUTE AS USER isn't supported for Azure AD users when the name differs from the login name. An example is when the user is created through the syntax CREATE USER [myAadUser] FROM LOGIN [john@contoso.com] and impersonation is attempted through EXEC AS USER = myAadUser. When you create a USER from an Azure AD server principal (login), specify the user_name as the same login_name from LOGIN.

    • Only the SQL Server-level principals (logins) that are part of the sysadmin role can execute the following operations that target Azure AD principals:

      • EXECUTE AS USER
      • EXECUTE AS LOGIN
  • Public preview limitations for Azure AD server principals (logins):

    • Active Directory admin limitations for managed instance:

      • The Azure AD admin used to set up the managed instance can't be used to create an Azure AD server principal (login) within the managed instance. You must create the first Azure AD server principal (login) by using a SQL Server account that's a sysadmin role. This temporary limitation will be removed after Azure AD server principals (logins) become generally available. If you try to use an Azure AD admin account to create the login, you see the following error: Msg 15247, Level 16, State 1, Line 1 User does not have permission to perform this action.

        • Currently, the first Azure AD login created in the master database must be created by the standard SQL Server account (non-Azure AD) that's a sysadmin role by using CREATE LOGIN FROM EXTERNAL PROVIDER. After general availability, this limitation will be removed. Then you can create an initial Azure AD login by using the Active Directory admin for managed instance.
      • DacFx (export/import) used with SQL Server Management Studio or SqlPackage isn't supported for Azure AD logins. This limitation will be removed after Azure AD server principals (logins) become generally available.

      • Using Azure AD server principals (logins) with SQL Server Management Studio:

        • Scripting Azure AD logins that use any authenticated login isn't supported.
        • IntelliSense doesn't recognize the CREATE LOGIN FROM EXTERNAL PROVIDER statement and shows a red underline.
  • Only the server-level principal login, which is created by the managed instance provisioning process, members of the server roles, such as securityadmin or sysadmin, or other logins with ALTER ANY LOGIN permission at the server level can create Azure AD server principals (logins) in the master database for managed instance.

  • If the login is a SQL principal, only logins that are part of the sysadmin role can use the create command to create logins for an Azure AD account.

  • The Azure AD login must be a member of an Azure AD within the same directory that's used for Azure SQL Database managed instance.

  • Azure AD server principals (logins) are visible in Object Explorer starting with SQL Server Management Studio 18.0 preview 5.

  • Overlapping Azure AD server principals (logins) with an Azure AD admin account is allowed. Azure AD server principals (logins) take precedence over the Azure AD admin when you resolve the principal and apply permissions to the managed instance.

  • During authentication, the following sequence is applied to resolve the authenticating principal:

    1. If the Azure AD account exists as directly mapped to the Azure AD server principal (login), which is present in sys.server_principals as type "E," grant access and apply permissions of the Azure AD server principal (login).
    2. If the Azure AD account is a member of an Azure AD group that's mapped to the Azure AD server principal (login), which is present in sys.server_principals as type "X," grant access and apply permissions of the Azure AD group login.
    3. If the Azure AD account is a special portal-configured Azure AD admin for managed instance, which doesn't exist in managed instance system views, apply special fixed permissions of the Azure AD admin for managed instance (legacy mode).
    4. If the Azure AD account exists as directly mapped to an Azure AD user in a database, which is present in sys.database_principals as type "E," grant access and apply permissions of the Azure AD database user.
    5. If the Azure AD account is a member of an Azure AD group that's mapped to an Azure AD user in a database, which is present in sys.database_principals as type "X," grant access and apply permissions of the Azure AD group login.
    6. If there's an Azure AD login mapped to either an Azure AD user account or an Azure AD group account, which resolves to the user who's authenticating, all permissions from this Azure AD login are applied.

Service key and service master key

Configuration

Buffer pool extension

Collation

The default instance collation is SQL_Latin1_General_CP1_CI_AS and can be specified as a creation parameter. See Collations.

Compatibility levels

  • Supported compatibility levels are 100, 110, 120, 130, and 140.
  • Compatibility levels below 100 aren't supported.
  • The default compatibility level for new databases is 140. For restored databases, the compatibility level remains unchanged if it was 100 and above.

See ALTER DATABASE Compatibility Level.

Database mirroring

Database mirroring isn't supported.

  • ALTER DATABASE SET PARTNER and SET WITNESS options aren't supported.
  • CREATE ENDPOINT … FOR DATABASE_MIRRORING isn't supported.

For more information, see ALTER DATABASE SET PARTNER and SET WITNESS and CREATE ENDPOINT … FOR DATABASE_MIRRORING.

Database options

  • Multiple log files aren't supported.
  • In-memory objects aren't supported in the General Purpose service tier.
  • There's a limit of 280 files per General Purpose instance, which implies a maximum of 280 files per database. Both data and log files in the General Purpose tier are counted toward this limit. The Business Critical tier supports 32,767 files per database.
  • The database can't contain filegroups that contain filestream data. Restore fails if .bak contains FILESTREAM data.
  • Every file is placed in Azure Blob storage. IO and throughput per file depend on the size of each individual file.

CREATE DATABASE statement

The following limitations apply to CREATE DATABASE:

  • Files and filegroups can't be defined.

  • The CONTAINMENT option isn't supported.

  • WITH options aren't supported.

    Tip

    As a workaround, use ALTER DATABASE after CREATE DATABASE to set database options to add files or to set containment.

  • The FOR ATTACH option isn't supported.

  • The AS SNAPSHOT OF option isn't supported.

For more information, see CREATE DATABASE.

ALTER DATABASE statement

Some file properties can't be set or changed:

  • A file path can't be specified in the ALTER DATABASE ADD FILE (FILENAME='path') T-SQL statement. Remove FILENAME from the script because a managed instance automatically places the files.
  • A file name can't be changed by using the ALTER DATABASE statement.

The following options are set by default and can't be changed:

  • MULTI_USER
  • ENABLE_BROKER ON
  • AUTO_CLOSE OFF

The following options can't be modified:

  • AUTO_CLOSE
  • AUTOMATIC_TUNING(CREATE_INDEX=ON|OFF)
  • AUTOMATIC_TUNING(DROP_INDEX=ON|OFF)
  • DISABLE_BROKER
  • EMERGENCY
  • ENABLE_BROKER
  • FILESTREAM
  • HADR
  • NEW_BROKER
  • OFFLINE
  • PAGE_VERIFY
  • PARTNER
  • READ_ONLY
  • RECOVERY BULK_LOGGED
  • RECOVERY_SIMPLE
  • REMOTE_DATA_ARCHIVE
  • RESTRICTED_USER
  • SINGLE_USER
  • WITNESS

For more information, see ALTER DATABASE.

SQL Server Agent

  • Enabling and disabling SQL Server Agent is currently not supported in managed instance. SQL Agent is always running.
  • SQL Server Agent settings are read only. The procedure sp_set_agent_properties isn't supported in managed instance.
  • Jobs
    • T-SQL job steps are supported.
    • The following replication jobs are supported:
      • Transaction-log reader
      • Snapshot
      • Distributor
    • SSIS job steps are supported.
    • Other types of job steps aren't currently supported:
      • The merge replication job step isn't supported.
      • Queue Reader isn't supported.
      • Command shell isn't yet supported.
    • Managed instances can't access external resources, for example, network shares via robocopy.
    • SQL Server Analysis Services aren't supported.
  • Notifications are partially supported.
  • Email notification is supported, although it requires that you configure a Database Mail profile. SQL Server Agent can use only one Database Mail profile, and it must be called AzureManagedInstance_dbmail_profile.
    • Pager isn't supported.
    • NetSend isn't supported.
    • Alerts aren't yet supported.
    • Proxies aren't supported.
  • EventLog isn't supported.

The following SQL Agent features currently aren't supported:

  • Proxies
  • Scheduling jobs on an idle CPU
  • Enabling or disabling an Agent
  • Alerts

For information about SQL Server Agent, see SQL Server Agent.

Tables

The following table types aren't supported:

For information about how to create and alter tables, see CREATE TABLE and ALTER TABLE.

Functionalities

Bulk insert / OPENROWSET

A managed instance can't access file shares and Windows folders, so the files must be imported from Azure Blob storage:

  • DATASOURCE is required in the BULK INSERT command while you import files from Azure Blob storage. See BULK INSERT.
  • DATASOURCE is required in the OPENROWSET function when you read the content of a file from Azure Blob storage. See OPENROWSET.

CLR

A managed instance can't access file shares and Windows folders, so the following constraints apply:

DBCC

Undocumented DBCC statements that are enabled in SQL Server aren't supported in managed instances.

  • Only a limited number of Global Trace flags is supported. Session-level Trace flags aren't supported. See Trace flags.
  • DBCC TRACEOFF and DBCC TRACEON work with the limited number of global trace-flags.
  • DBCC CHECKDB with options REPAIR_ALLOW_DATA_LOSS, REPAIR_FAST, and REPAIR_REBUILD cannot be used because database cannot be set in SINGLE_USER mode - see ALTER DATABASE differences. Potential database corruptions are handled by Azure support team. Contact Azure support if you are noticing database corruption that should be fixed.

Distributed transactions

MSDTC and elastic transactions currently aren't supported in managed instances.

Extended Events

Some Windows-specific targets for Extended Events (XEvents) aren't supported:

  • The etw_classic_sync target isn't supported. Store .xel files in Azure Blob storage. See etw_classic_sync target.
  • The event_file target isn't supported. Store .xel files in Azure Blob storage. See event_file target.

External libraries

In-database R and Python, external libraries aren't yet supported. See SQL Server Machine Learning Services.

Filestream and FileTable

  • Filestream data isn't supported.
  • The database can't contain filegroups with FILESTREAM data.
  • FILETABLE isn't supported.
  • Tables can't have FILESTREAM types.
  • The following functions aren't supported:
    • GetPathLocator()
    • GET_FILESTREAM_TRANSACTION_CONTEXT()
    • PathName()
    • GetFileNamespacePat)
    • FileTableRootPath()

For more information, see FILESTREAM and FileTables.

Semantic Search isn't supported.

Linked servers

Linked servers in managed instances support a limited number of targets:

  • Supported targets are Managed Instances, Single Databases, and SQL Server instances.
  • Linked servers don't support distributed writable transactions (MS DTC).
  • Targets that aren't supported are files, Analysis Services, and other RDBMS. Try to use native CSV import from Azure Blob Storage using BULK INSERT or OPENROWSET as an alternative for file import.

Operations

  • Cross-instance write transactions aren't supported.
  • sp_dropserver is supported for dropping a linked server. See sp_dropserver.
  • The OPENROWSET function can be used to execute queries only on SQL Server instances. They can be either managed, on-premises, or in virtual machines. See OPENROWSET.
  • The OPENDATASOURCE function can be used to execute queries only on SQL Server instances. They can be either managed, on-premises, or in virtual machines. Only the SQLNCLI, SQLNCLI11, and SQLOLEDB values are supported as a provider. An example is SELECT * FROM OPENDATASOURCE('SQLNCLI', '...').AdventureWorks2012.HumanResources.Employee. See OPENDATASOURCE.
  • Linked servers cannot be used to read files (Excel, CSV) from the network shares. Try to use BULK INSERT or OPENROWSET that reads CSV files from Azure Blob Storage. Track this requests on managed instance Feedback item|

PolyBase

External tables that reference the files in HDFS or Azure Blob storage aren't supported. For information about PolyBase, see PolyBase.

Replication

  • Snapshot and Bi-directional replication types are supported. Merge replication, Peer-to-peer replication, and updatable subscriptions are not supported.
  • Transactional Replication is available for public preview on managed instance with some constraints:
    • All types of replication participants (Publisher, Distributor, Pull Subscriber, and Push Subscriber) can be placed on managed instances, but Publisher and Distributor cannot be placed on different instances.
    • Managed instances can communicate with the recent versions of SQL Server. See the supported versions here.
    • Transactional Replication has some additional networking requirements.

For information about configuring replication, see the replication tutorial.

If replication is enabled on a database in a failover group, the managed instance administrator must cleanup all publications on the old primary and reconfigure them on the new primary after a failover occurs. The following activities are needed in this scenario:

  1. Stop all replication jobs running on the database, if there are any.

  2. Drop subscription metadata from publisher by running the following script on publisher database:

    EXEC sp_dropsubscription @publication='<name of publication>', @article='all',@subscriber='<name of subscriber>'
    
  3. Drop subscription metadata from the subscriber. Run the following script in the subscription database on subscriber instance:

    EXEC sp_subscription_cleanup
       @publisher = N'<full DNS of publisher, e.g. example.ac2d23028af5.database.windows.net>', 
       @publisher_db = N'<publisher database>', 
       @publication = N'<name of publication>'; 
    
  4. Forcefully drop all replication objects from publisher by running the following script in the published database:

    EXEC sp_removedbreplication
    
  5. Forcefully drop old distributor from original primary instance (if failing back over to an old primary that used to have a distributor). Run the following script on the master database in old distributor managed instance:

    EXEC sp_dropdistributor 1,1
    

RESTORE statement

  • Supported syntax:
    • RESTORE DATABASE
    • RESTORE FILELISTONLY ONLY
    • RESTORE HEADER ONLY
    • RESTORE LABELONLY ONLY
    • RESTORE VERIFYONLY ONLY
  • Unsupported syntax:
    • RESTORE LOG ONLY
    • RESTORE REWINDONLY ONLY
  • Source:
    • FROM URL (Azure Blob storage) is the only supported option.
    • FROM DISK/TAPE/backup device isn't supported.
    • Backup sets aren't supported.
  • WITH options aren't supported, such as no DIFFERENTIAL or STATS.
  • ASYNC RESTORE: Restore continues even if the client connection breaks. If your connection is dropped, you can check the sys.dm_operation_status view for the status of a restore operation, and for a CREATE and DROP database. See sys.dm_operation_status.

The following database options are set or overridden and can't be changed later:

  • NEW_BROKER if the broker isn't enabled in the .bak file.
  • ENABLE_BROKER if the broker isn't enabled in the .bak file.
  • AUTO_CLOSE=OFF if a database in the .bak file has AUTO_CLOSE=ON.
  • RECOVERY FULL if a database in the .bak file has SIMPLE or BULK_LOGGED recovery mode.
  • A memory-optimized filegroup is added and called XTP if it wasn't in the source .bak file.
  • Any existing memory-optimized filegroup is renamed to XTP.
  • SINGLE_USER and RESTRICTED_USER options are converted to MULTI_USER.

Limitations:

  • Backups of the corrupted databases might be restored depending on the type of the corruption, but automated backups will not be taken until the corruption is fixed. Make sure that you run DBCC CHECKDB on the source instance and use backup WITH CHECKSUM in order to prevent this issue.
  • Restore of .BAK file of a database that contains any limitation described in this document (for example, FILESTREAM or FILETABLE objects) cannot be restored on Managed Instance.
  • .BAK files that contain multiple backup sets can't be restored.
  • .BAK files that contain multiple log files can't be restored.
  • Backups that contain databases bigger than 8TB, active in-memory OLTP objects, or more than 280 files can't be restored on a General Purpose instance.
  • Backups that contain databases bigger than 4TB or in-memory OLTP objects with the total size larger than the size described in resource limits cannot be restored on Business Critical instance. For information about restore statements, see RESTORE statements.

Service broker

Cross-instance service broker isn't supported:

  • sys.routes: As a prerequisite, you must select the address from sys.routes. The address must be LOCAL on every route. See sys.routes.
  • CREATE ROUTE: You can't use CREATE ROUTE with ADDRESS other than LOCAL. See CREATE ROUTE.
  • ALTER ROUTE: You can't use ALTER ROUTE with ADDRESS other than LOCAL. See ALTER ROUTE.

Stored procedures, functions, and triggers

Environment constraints

Subnet

VNET

  • VNet can be deployed using Resource Model - Classic Model for VNet is not supported.
  • After a managed instance is created, moving the managed instance or VNet to another resource group or subscription is not supported.
  • Some services such as App Service Environments, Logic apps, and managed instances (used for Geo-replication, Transactional replication, or via linked servers) cannot access managed instances in different regions if their VNets are connected using global peering. You can connect to these resources via ExpressRoute or VNet-to-VNet through VNet Gateways.

TEMPDB size

The maximum file size of tempdb can't be greater than 24 GB per core on a General Purpose tier. The maximum tempdb size on a Business Critical tier is limited by the instance storage size. Tempdb log file size is limited to 120 GB both on General Purpose and Business Critical tiers. Some queries might return an error if they need more than 24 GB per core in tempdb or if they produce more than 120 GB of log data.

Behavior changes

The following variables, functions, and views return different results:

  • SERVERPROPERTY('EngineEdition') returns the value 8. This property uniquely identifies a managed instance. See SERVERPROPERTY.
  • SERVERPROPERTY('InstanceName') returns NULL because the concept of instance as it exists for SQL Server doesn't apply to a managed instance. See SERVERPROPERTY('InstanceName').
  • @@SERVERNAME returns a full DNS "connectable" name, for example, my-managed-instance.wcus17662feb9ce98.database.windows.net. See @@SERVERNAME.
  • SYS.SERVERS returns a full DNS "connectable" name, such as myinstance.domain.database.windows.net for the properties "name" and "data_source." See SYS.SERVERS.
  • @@SERVICENAME returns NULL because the concept of service as it exists for SQL Server doesn't apply to a managed instance. See @@SERVICENAME.
  • SUSER_ID is supported. It returns NULL if the Azure AD login isn't in sys.syslogins. See SUSER_ID.
  • SUSER_SID isn't supported. The wrong data is returned, which is a temporary known issue. See SUSER_SID.

Known issues and limitations

Cross-database Service Broker dialogs don't work after service tier upgrade

Date: Aug 2019

Cross-database Service Broker dialogs fail to deliver the messages after change service tier operation. Any change of vCores or instance storage size in Managed Instance, will cause service_broke_guid value in sys.databases view to be changed for all databases. Any DIALOG created using BEGIN DIALOG statement that references Service Brokers in other database by GUID, will not be able to deliver messages.

Workaround: Stop any activity that uses cross-database Service Broker dialog conversations before updating service tier and re-initialize them after.

Some AAD login types cannot be impersonated

Date: July 2019

Impersonation using EXECUTE AS USER or EXECUTE AS LOGIN of following AAD principals is not supported:

  • Aliased AAD users. The following error is returned in this case 15517.
  • AAD logins and users based on AAD applications or service principals. The following errors are returned in this case 15517 and 15406.

@query parameter not supported in sp_send_db_mail

Date: April 2019

The @query parameter in the sp_send_db_mail procedure doesn't work.

AAD logins and users are not supported in tools

Date: Jan 2019

SQL Server Management Studio and SQL Server Data Tools don't fuly support Azure Acctive directory logins and users.

  • Using Azure AD server principals (logins) and users (public preview) with SQL Server Data Tools currently isn't supported.
  • Scripting for Azure AD server principals (logins) and users (public preview) isn't supported in SQL Server Management Studio.

TEMPDB structure and content is re-created

The tempdb database is always split into 12 data files and the file structure cannot be changed. The maximum size per file can't be changed, and new files cannot be added to tempdb. Tempdb is always re-created as an empty database when the instance starts or fails over, and any changes made in tempdb will not be preserved.

Exceeding storage space with small database files

CREATE DATABASE, ALTER DATABASE ADD FILE, and RESTORE DATABASE statements might fail because the instance can reach the Azure Storage limit.

Each General Purpose managed instance has up to 35 TB of storage reserved for Azure Premium Disk space. Each database file is placed on a separate physical disk. Disk sizes can be 128 GB, 256 GB, 512 GB, 1 TB, or 4 TB. Unused space on the disk isn't charged, but the total sum of Azure Premium Disk sizes can't exceed 35 TB. In some cases, a managed instance that doesn't need 8 TB in total might exceed the 35 TB Azure limit on storage size due to internal fragmentation.

For example, a General Purpose managed instance might have one big file that's 1.2 TB in size placed on a 4-TB disk. It also might have 248 files 1GB files that are each placed on separate 128-GB disks. In this example:

  • The total allocated disk storage size is 1 x 4 TB + 248 x 128 GB = 35 TB.
  • The total reserved space for databases on the instance is 1 x 1.2 TB + 248 x 1 GB = 1.4 TB.

This example illustrates that under certain circumstances, due to a specific distribution of files, a managed instance might reach the 35-TB limit that's reserved for an attached Azure Premium Disk when you might not expect it to.

In this example, existing databases continue to work and can grow without any problem as long as new files aren't added. New databases can't be created or restored because there isn't enough space for new disk drives, even if the total size of all databases doesn't reach the instance size limit. The error that's returned in that case isn't clear.

You can identify the number of remaining files by using system views. If you reach this limit, try to empty and delete some of the smaller files by using the DBCC SHRINKFILE statement or switch to the Business Critical tier, which doesn't have this limit.

GUID values shown instead of database names

Several system views, performance counters, error messages, XEvents, and error log entries display GUID database identifiers instead of the actual database names. Don't rely on these GUID identifiers because they're replaced with actual database names in the future.

Error logs aren't persisted

Error logs that are available in managed instance aren't persisted, and their size isn't included in the maximum storage limit. Error logs might be automatically erased if failover occurs.

Error logs are verbose

A managed instance places verbose information in error logs, and much of it isn't relevant.

Workaround: Use a custom procedure to read error logs that filters out some irrelevant entries. For more information, see managed instance – sp_readmierrorlog.

Transaction scope on two databases within the same instance isn't supported

The TransactionScope class in .NET doesn't work if two queries are sent to two databases within the same instance under the same transaction scope:

using (var scope = new TransactionScope())
{
    using (var conn1 = new SqlConnection("Server=quickstartbmi.neu15011648751ff.database.windows.net;Database=b;User ID=myuser;Password=mypassword;Encrypt=true"))
    {
        conn1.Open();
        SqlCommand cmd1 = conn1.CreateCommand();
        cmd1.CommandText = string.Format("insert into T1 values(1)");
        cmd1.ExecuteNonQuery();
    }

    using (var conn2 = new SqlConnection("Server=quickstartbmi.neu15011648751ff.database.windows.net;Database=b;User ID=myuser;Password=mypassword;Encrypt=true"))
    {
        conn2.Open();
        var cmd2 = conn2.CreateCommand();
        cmd2.CommandText = string.Format("insert into b.dbo.T2 values(2)");        cmd2.ExecuteNonQuery();
    }

    scope.Complete();
}

Although this code works with data within the same instance, it required MSDTC.

Workaround: Use SqlConnection.ChangeDatabase(String) to use another database in a connection context instead of using two connections.

CLR modules and linked servers sometimes can't reference a local IP address

CLR modules placed in a managed instance and linked servers or distributed queries that reference a current instance sometimes can't resolve the IP of a local instance. This error is a transient issue.

Workaround: Use context connections in a CLR module if possible.

Next steps