Azure SQL Managed Instance vs SQL Server On-Premises

Compare Azure SQL MI vs On-Premises

Features

Azure SQL Managed Instance

SQL Server On-Premises

Deployment

Created via Azure portal in a VNet; a few hours to provision fully, but minimal user config (Azure sets up SQL).

Provision hardware/VMs and install OS and SQL – slowest option, entirely manual (weeks to procure if new hardware).

Management

Fully managed by Azure – patching, updates, backups handled by service.

Fully self-managed by your IT team (complete responsibility for maintenance).

Customization

Restricted – cannot access OS or certain features; limited to options Azure exposes (instance size, certain settings).

Unlimited – choose any hardware, OS, SQL configuration (most flexible).

Use Case

Best for migrating on-prem apps to Azure with minimal changes, needing instance-level features (Agent, cross-DB) but wanting a managed service.

Ideal for strict data control, low-latency to on-prem apps, or existing data center investments; also when compliance or legacy systems mandate it.

Maintenance Responsibility

Microsoft – Azure automatically patches OS and SQL engine (with almost no downtime).

Your IT team entirely – on-prem requires internal processes for all updates.

Operational Control

Partial – you have instance-level admin in SQL, but no OS access and some server-level permissions are restricted by Azure.

Complete control at hardware, OS, and DB level – no restrictions (can even delay patches indefinitely, for example).

Backups

Automated: Azure performs continuous backups (point-in-time restore up to 35 days); user can initiate extra backups to storage for long-term.

Completely on user – typically use maintenance plans or enterprise backup tools writing to tapes/cloud.

Scalability

Vertical: change vCore count (online resize with brief disruption); Horizontal: limited – one primary instance, can add geo-replicas for read/DR (no multiple writable instances).

Vertical: buy/upgrade hardware (major project); Horizontal: add servers and distribute load (requires significant effort and maybe app changes).

Performance

Very good for most cases: GP tier ~ “disk over network” latency (~5-10ms) and up to ~80k IOPS at max vCores, BC tier ~ “local SSD” latency (1-2ms) and up to ~320k IOPS at max size; Azure manages performance, but you might not reach extreme on-prem levels for edge cases.

Potentially the highest (you can use top-end hardware, dedicated storage arrays, etc.); ultimate performance if budget allows, with no virtualization overhead if physical.

Elasticity

No auto-scale of vCores on-the-fly; you must manually scale up/down. However, you can add/remove Managed Instances in a pool (instance pools) if using that model for multi-instance elasticity, but that’s more static allocation of multiple MIs.

None – capacity is fixed once purchased. Scaling requires planning and manual execution (or new hardware purchase).

SQL Server Version

Azure handles the version – effectively it’s the latest SQL Server engine (currently equivalent to 2019/2022). You can’t choose an older engine version, but you can set database compatibility level down to 100 (SQL 2008) for legacy T-SQL compatibility.

Any version/edition for which you have media and license – including very old versions (some orgs still run 2008 or 2005 for legacy apps, which on-prem allows, albeit unsupported by MS).

SQL Feature Support

Yes, one of MI’s advantages over Azure SQL DB – you can do three-part naming queries across databases on the instance, and even cross-instance via linked servers (within some constraints of managed env).

Everything SQL Server offers is available if you set it up – including things like replication, Linked Servers, Service Broker, etc. You have to configure them, but nothing is disabled by a provider.

Cross-Database Queries

Yes, common on on-prem to have many DBs on one server and join them. Also, cross-server via linked server is possible.

Custom Software

No – you cannot RDP into the instance or install anything. CLR assemblies are allowed in SAFE mode within SQL (no external access), but you can’t install a custom extensibility framework or third-party utility on the server. Integration with other services must be done externally over network.

Yes – common to have monitoring agents (SCOM, etc.) on SQL servers, or backup agents. You could even run a third-party application on the same machine (though best practice is to separate, it’s up to you).

Network Configuration

Deployed into your VNet (requires a dedicated subnet)– it gets a private IP. You manage NSGs for that subnet. By default no public endpoint (optionally can enable one). It’s like a managed appliance sitting in your network.

On your corporate network – ultimate control (your own firewall, switches, VLANs). You can make it as open or isolated as you need. Typically behind corporate firewalls and accessible only within company network.

Security

Platform-managed security: TDE on by default, backups encrypted. Azure manages OS security patches. You can use Azure AD authentication for tighter identity control. MI is deployed in your private network, adding an extra layer of isolation. It meets Azure’s compliance standards out-of-the-box (you just focus on DB-level security like user permissions).

Entirely on you – from physical security of the server room, to network security, to OS and SQL security. You can achieve very high security (even completely air-gapped networks), but it requires strict processes. Encryption (TDE, etc.) must be configured by you.

Authentication

SQL Auth and Azure Active Directory Auth supported. You set an AAD admin and then you can use AAD users/groups as logins. No direct Windows AD integration (would need to sync AD to AAD). This gives centralized cloud identity management for the MI.

Windows Auth and SQL Auth – often tightly integrated with on-prem AD. You can enforce AD group policies, etc. If not on a domain, SQL Auth is used. No cloud-specific auth out of the box (though you could integrate Kerberos and AD FS if needed for fancy setups).

High Availability

Built-in: MI (Business Critical) has HA with automatic failover of the primary replica to a secondary if something happens (Azure handles it). General Purpose has Azure Service Fabric-based failover using remote storage. Either way, you get an SLA for HA without configuring clustering yourself.

Many options but all manual: Failover Cluster Instances (with shared storage like SAN), Always On AG, database mirroring (old), log shipping as quasi-HA. Requires redundant hardware and networking. You manage failover process (though AG can auto-failover).

Disaster Recovery

Easy DR: you can configure a geo-replica MI in another region (Auto-failover Group). This will asynchronously replicate all databases. Failover can be automatic (for groups) or manual. If you choose not to have a second MI, you still have geo-redundant backups which you could restore in another region (slower recovery).

Entirely on you: could be as robust as a secondary data center with log shipping or AGs, or as basic as offsite backup tapes. DR testing and execution are your ops team’s duty.

Pricing

Azure SQL MI pricing is per vCore, per hour, plus storage and backup costs. An 8 vCore General Purpose instance with 4TB follows an hourly compute + per-GB-month storage model. Business Critical costs 2-3× more per vCore due to faster hardware and extra replicas. SQL licensing is included.

Big upfront CapEx for hardware & licenses, then minor OpEx (power, cooling). Amortized 3-year cost for an 8-core server might be ~$1-3k/month depending on edition (Standard vs Enterprise), but you own the asset. Scaling requires new investment.

Licensing Model

Azure SQL MI supports License-Included or Azure Hybrid Benefit, which lowers costs if you bring SQL Server licenses with Software Assurance. Reserved Capacity (1-3 years) offers discounts over pay-as-you-go.

Perpetual or Subscription licenses. Typically purchase per core (Enterprise ~$7.5k/core, Standard ~$1.9k/core) plus optional SA ~25%/yr. Hardware bought or leased separately. No builtin pay-per-use; however, you could run SQL Developer or Express free in non-prod.

Pricing Comparison of Database Configuration

8vCore + 4TB Data size + Backup,  Single Instance

An 8 vCore, 4TB General Purpose Azure SQL MI in East US costs $1,700–$2,000/month ($1,300 compute + $400 storage). Hybrid Benefit can reduce compute costs by 30-40%.

On-prem not monthly billed, but roughly ~$1k (Std) / ~$3k (Ent) per month value when spread over a few years.

8vCore + 4TB Data size + Backup + DR/HA

A second 8-vCore MI (Auto-Failover Group) doubles the cost to $3,500–$4,000/month. If using Business Critical, an 8 vCore, 4TB instance costs $5,000+ per month, including 3 built-in replicas (no extra VM needed for HA).

Multi-site on-prem: requires second set of hardware (and possibly second license if active-active).
Hard to monthly-ize, but essentially 2× hardware cost; SQL license for passive is free with SA.