Azure SQL Managed Instance

Azure SQL Managed Instance is a fully managed deployment option for SQL Server that provides near-100% compatibility with the on-premises SQL Server engine. It is designed specifically for organisations that need to migrate existing SQL Server workloads to Azure without rewriting applications.

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Why SQL Managed Instance?

Azure SQL Database is excellent for new cloud-native applications, but some existing workloads rely on SQL Server features that Azure SQL Database does not support. SQL Managed Instance bridges this gap:

Feature	Azure SQL Database	SQL Managed Instance
SQL Server Agent	Not available	Supported
Cross-database queries	Not available	Supported
CLR integration	Not available	Supported
Linked servers	Not available	Supported
Service Broker	Not available	Supported
Database mail	Not available	Supported
Native backup/restore	Not supported	Supported
VNet deployment	Firewall rules / Private Endpoint	Native VNet integration
Instance-scoped features	Limited	Full instance scope

If your migration assessment identifies dependencies on any of these features, SQL Managed Instance is the recommended target.

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Architecture

SQL Managed Instance runs inside a managed virtual cluster within your Azure Virtual Network:

Your Virtual Network
  |
  |-- Managed Instance Subnet (dedicated, delegated to SQL MI)
        |
        |-- SQL Managed Instance
              |-- Database A
              |-- Database B
              |-- Database C
              |-- tempdb, master, msdb, model (system databases)

Key Architecture Points

• The subnet is delegated to the SQL Managed Instance service — no other resources can be deployed in it
• The subnet requires a minimum of /27 CIDR (32 addresses) but /24 is recommended for flexibility
• Network Security Groups (NSGs) and User-Defined Routes (UDRs) can be applied to the subnet
• A public endpoint is available but disabled by default — access is typically through the VNet

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Service Tiers

General Purpose

Feature	Detail
Storage	Azure Premium Storage (remote)
Max storage	16 TB
vCores	4–80
Availability	99.99% SLA
Use case	Most business workloads

Business Critical

Feature	Detail
Storage	Local SSD
Max storage	4 TB
vCores	4–80
Availability	99.99% SLA
Built-in read replica	One free read-only replica
In-memory OLTP	Supported
Use case	Low-latency, high-throughput workloads

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Migration Methods

Native Backup and Restore

The simplest migration path for many workloads:

1. Back up your on-premises database to Azure Blob Storage
2. Restore from the blob URL into your Managed Instance

-- Restore from Azure Blob Storage
RESTORE DATABASE MyDatabase
FROM URL = 'https://mystorageaccount.blob.core.windows.net/backups/MyDatabase.bak'
WITH MOVE 'MyDatabase' TO '/var/opt/mssql/data/MyDatabase.mdf',
     MOVE 'MyDatabase_log' TO '/var/opt/mssql/data/MyDatabase_log.ldf';

Azure Database Migration Service (DMS)

For online migrations with minimal downtime:

1. DMS performs an initial full backup and restore
2. DMS continuously applies transaction log backups from the source
3. When you are ready, perform the cutover (typically seconds of downtime)

Log Replay Service

An alternative for online migration: