Overview of Azure SQL Managed Instance resource limits

Applies to: Azure SQL Managed Instance

This article provides an overview of the technical characteristics and resource limits for Azure SQL Managed Instance, and provides information about how to request an increase to these limits.

Note

For differences in supported features and T-SQL statements see Feature differences and T-SQL statement support. For general differences between service tiers for Azure SQL Database and SQL Managed Instance review General Purpose and Business Critical service tiers.

Hardware configuration characteristics

SQL Managed Instance has characteristics and resource limits that depend on the underlying infrastructure and architecture. SQL Managed Instance can be deployed on multiple hardware generations.

Note

The Gen5 hardware has been renamed to the standard-series (Gen5).

Hardware generations have different characteristics, as described in the following table:

Standard-series (Gen5) Premium-series Memory optimized premium-series
CPU Intel® E5-2673 v4 (Broadwell) 2.3 GHz, Intel® SP-8160 (Skylake), and Intel® 8272CL (Cascade Lake) 2.5 GHz processors Intel® 8370C (Ice Lake) 2.8 GHz processors Intel® 8370C (Ice Lake) 2.8 GHz processors
Number of vCores
vCore=1 LP (hyper-thread)
21-80 vCores 21-128 vCores 4-128 vCores
Max memory (memory/vCore ratio) 5.1 GB per vCore - 408 GB maximum
Add more vCores to get more memory.
7 GB per vCore up to 80 vCores - 560 GB maximum 13.6 GB per vCore up to 64 vCores - 870.4 GB maximum
Max In-Memory OLTP memory Instance limit: 0.8 - 1.65 GB per vCore Instance limit: 1.1 - 2.3 GB per vCore Instance limit: 2.2 - 4.5 GB per vCore
Max instance reserved storage2 General Purpose: up to 16 TB
Business Critical: up to 4 TB
General Purpose: up to 16 TB
Business Critical: up to 5.5 TB
General Purpose: up to 16 TB
Business Critical: up to 16 TB

1 Deploying a 2-vCore instance is only possible inside an instance pool.
2 Dependent on the number of vCores.

Note

If your workload requires storage sizes greater than the available resource limits for Azure SQL Managed Instance, consider the Azure SQL Database Hyperscale service tier.

Regional supports for memory optimized premium-series hardware and for premium-series hardware with 16 TB storage

Support for the premium-series hardware with 16 TB storage has the same availability as support for the memory optimized premium-series hardware. Supports for the memory-optimized premium-series hardware and the premium-series hardware with 16 TB storage are currently available only in these specific regions:

Geography Regions supporting memory optimized premium-series HW and premium-series hardware with 16 TB Storage
Europe France Central, Germany West Central, Italy North, North Europe, Poland Central, Sweden Central, Switzerland North, UK South, West Europe
Middle East, Africa Qatar Central
Americas Brazil South, Canada Central, Central US, East US, East US 2, North Central US, South Central US, West US, West US 2, West US 3
Asia Pacific Australia East, Australia Southeast, China North 3, India Central, India South, East Asia, Japan East, Southeast Asia

In-memory OLTP available space

The amount of In-memory OLTP space in Business Critical service tier depends on the number of vCores and hardware configuration. The following table lists the limits of memory that can be used for In-memory OLTP objects.

vCores Standard-series (Gen5) Premium-series Memory optimized premium-series
4 vCores 3.14 GB 4.39 GB 8.79 GB
6 vCores - 6.59 GB 15.32 GB
8 vCores 6.28 GB 8.79 GB 22.06 GB
10 vCores - 12.11 GB 30.94 GB
12 vCores - 15.43 GB 39.82 GB
16 vCores 15.77 GB 22.06 GB 57.58 GB
20 vCores - 28.70 GB 75.34 GB
24 vCores 25.25 GB 35.34 GB 93.09 GB
32 vCores 37.94 GB 53.09 GB 128.61 GB
40 vCores 52.23 GB 73.09 GB 164.13 GB
48 vCores - 95.34 GB 199.64 GB
56 vCores - 117.58 GB 244.13 GB
64 vCores 99.9 GB 139.82 GB 288.61 GB
80 vCores 131.68 GB 184.30 GB 288.61 GB
96 vCores N/A 184.30 GB 288.61 GB
128 vCores N/A 184.30 GB 288.61 GB

Service tier characteristics

SQL Managed Instance has two service tiers: General Purpose and Business Critical.

Important

The Business Critical service tier provides an additional built-in copy of the SQL Managed Instance (secondary replica) that can be used for read-only workload. If you can separate read-write queries and read-only/analytic/reporting queries, you are getting twice the vCores and memory for the same price. The secondary replica might lag a few seconds behind the primary instance, so it is designed to offload reporting/analytic workloads that don't need exact current state of data. In the following table, read-only queries are the queries that are executed on secondary replica.

Feature General Purpose Business Critical
Number of vCores* 21, 4, 8, 16, 24, 32, 40, 64, 80 Standard-series (Gen5): 4, 8, 16, 24, 32, 40, 64, 80
Premium-series: 4, 6, 8, 10, 12, 16, 20, 24, 32, 40, 48, 56, 64, 80, 962, 1282
Memory optimized premium-series: 4, 6, 8, 10, 12, 16, 20, 24, 32, 40, 48, 56, 64, 802, 962, 1282
*Same number of vCores is dedicated for read-only queries.
Max memory Standard-series (Gen5): 20.4 GB - 408 GB (5.1 GB/vCore)
Premium-series: 28 GB - 560 GB (7 GB/vCore)
Memory optimized premium-series: 54.4 GB - 870.4 GB (13.6 GB/vCore)
Standard-series (Gen5): 20.4 GB - 408 GB (5.1 GB/vCore) on each replica
Premium-series: 28 GB - 560 GB (7 GB/vCore up to 80 vCores2) on each replica
Memory optimized premium-series: 54.4 GB - 870.4 GB (13.6 GB/vCore up to 64 vCores2) on each replica
Max instance storage size (reserved) - 2 TB for 4 vCores
- 8 TB for 8 vCores
- 16 TB for other sizes
Standard-series (Gen5):
- 1 TB for 4, 8, 16 vCores
- 2 TB for 24 vCores
- 4 TB for 32, 40, 64, 80 vCores
Premium-series:
- 1 TB for 4, 6 vCores
- 2 TB for 8, 10, 12 vCores
- 4 TB for 16, 20 vCores
- 5.5 TB for 24, 32, 40, 48, 56 vCores
- 5.5 TB or 16 TB (depending on the region) for 64, 80, 96, 128 vCores3
Memory optimized premium-series:
- 1 TB for 4, 6 vCores
- 2 TB for 8, 10, 12 vCores
- 4 TB for 16, 20 vCores
- 5.5 TB for 24 vCores
- 5.5 TB or 8 TB (depending on the region) for 32, 40 vCores4
- 12 TB for 48, 56 vCores
- 16 TB for 64, 80, 96, 128 vCores
Max database size Up to currently available instance size (depending on the number of vCores). Up to currently available instance size (depending on the number of vCores).
Max tempdb database size Limited to 24 GB/vCore (96 - 1,920 GB) and currently available instance storage size.
Add more vCores to get more tempdb space.
Log file size is limited to 120 GB.
Up to currently available instance storage size.
Max number of tempdb files 128 128
Max number of databases per instance 100 user databases, unless the instance storage size limit has been reached. 100 user databases, unless the instance storage size limit has been reached.
Max number of database files 280 per instance, unless the instance storage size or Azure Premium Disk storage allocation space limit has been reached. 32,767 files per database, unless the instance storage size limit has been reached.
Max data file size Maximum size of each data file is 8 TB. Use at least two data files for databases larger than 8 TB. Up to currently available instance size (depending on the number of vCores).
Max log file size Limited to 2 TB and currently available instance storage size. Limited to 2 TB and currently available instance storage size.
Data/Log IOPS (approximate) 500 - 7500 per file
*Increase file size to get more IOPS
16 K - 320 K (4000 IOPS/vCore)
Add more vCores to get better IO performance.
Log write throughput limit (per instance) 4.5 MiB/s per vCore
Max 120 MiB/s per instance
22 - 65 MiB/s per DB (depending on log file size)
*Increase the file size to get better IO performance
4.5 MiB/s per vCore
Max 192 MiB/s
Data throughput (approximate) 100 - 250 MiB/s per file
*Increase the file size to get better IO performance
Not limited.
Storage IO latency (approximate) 5-10 ms 1-2 ms
In-memory OLTP Not supported Available, size depends on number of vCore
Max sessions 30000 30000
Max concurrent workers 105 * number of vCores + 800 105 * number of vCores + 800
Read-only replicas 0 1 (included in price)
Compute isolation Not supported as General Purpose instances may share physical hardware with other instances Standard-series (Gen5):
Supported for configurations with 64 or more vCores
Premium-series: Supported for configurations with 64 or more vCores
Memory optimized premium-series: Supported for configurations with 64 or more vCores

1 Deploying a 2-vCore instance is only possible inside an instance pool.
2 The memory-to-vCore ratio is only available up to 80 vCores for premium-series hardware, and 64 vCores for memory optimized premium-series. Maximum memory is capped at 560 GB for premium-series vCores above 80, and 870.4 GB for memory optimized premium-series vCores above 64.
3 Only in the major regions can provide 16 TB of storage for the premium-series hardware for these CPU vCore numbers, the smaller regions will be limiting with available storage with 5.5 TB.
4 Only in the major regions can provide 8 TB of storage for the premium-series memory optimized hardware for these CPU vCore numbers, the smaller regions will be limiting with available storage with 5.5 TB.

A few additional considerations:

  • Currently available instance storage size is the difference between reserved instance size and the used storage space.
  • Both data and log file size in the user and system databases are included in the instance storage size that is compared with the max storage size limit. Use the sys.master_files system view to determine the total used space by databases. Error logs are not persisted and not included in the size. Backups are not included in storage size.
  • Throughput and IOPS in the General Purpose tier also depend on the file size that is not explicitly limited by the SQL Managed Instance. You can create another readable replica in a different Azure region using failover groups
  • Max instance IOPS depend on the file layout and distribution of workload. As an example, if you create 7 x 1-TB files with max 5 K IOPS each and seven small files (smaller than 128 GB) with 500 IOPS each, you can get 38500 IOPS per instance (7x5000+7x500) if your workload can use all files. Note that some IOPS are also used for auto-backups.
  • Names of tempdbfiles cannot have more than 16 characters.

Find more information about the resource limits in SQL Managed Instance pools in this article.

Data and log storage

The following factors affect the amount of storage used for data and log files, and apply to General Purpose and Business Critical tiers.

  • In the General Purpose service tier, tempdb uses local SSD storage, and this storage cost is included in the vCore price.
  • In the Business Critical service tier, tempdb shares local SSD storage with data and log files, and tempdb storage cost is included in the vCore price.
  • The maximum storage size for a SQL Managed Instance must be specified in multiples of 32 GB.

Important

In both service tiers, you are charged for the maximum storage size configured for a managed instance.

To monitor total consumed instance storage size for SQL Managed Instance, use the storage_space_used_mb metric. To monitor the current allocated and used storage size of individual data and log files in a database using T-SQL, use the sys.database_files view and the FILEPROPERTY(... , 'SpaceUsed') function.

Tip

Under some circumstances, you may need to shrink a database to reclaim unused space. For more information, see DBCC SHRINKFILE.

Backups and storage

Storage for database backups is allocated to support the point-in-time restore (PITR) and long-term retention (LTR) capabilities of SQL Managed Instance. This storage is separate from data and log file storage, and is billed separately.

  • PITR: In General Purpose and Business Critical tiers, individual database backups are copied to read-access geo-redundant (RA-GRS) storage automatically. The storage size increases dynamically as new backups are created. The storage is used by full, differential, and transaction log backups. The storage consumption depends on the rate of change of the database and the retention period configured for backups. You can configure a separate retention period for each database between 1 to 35 days for SQL Managed Instance. A backup storage amount equal to the configured maximum data size is provided at no extra charge.
  • LTR: You also have the option to configure long-term retention of full backups for up to 10 years. If you set up an LTR policy, these backups are stored in RA-GRS storage automatically, but you can control how often the backups are copied. To meet different compliance requirements, you can select different retention periods for weekly, monthly, and/or yearly backups. The configuration you choose determines how much storage will be used for LTR backups. For more information, see Long-term backup retention.

File IO characteristics in General Purpose tier

In the General Purpose service tier, every database file gets dedicated IOPS and throughput that depend on the file size. Larger files get more IOPS and throughput. IO characteristics of database files are shown in the following table:

File size >=0 and <=129 GiB >129 and <=513 GiB >513 and <=1025 GiB >1025 and <=2049 GiB >2049 and <=4097 GiB >4097 GiB and <=8 TiB
IOPS per file 500 2300 5000 7500 7500 7500
Throughput per file 100 MiB/s 150 MiB/s 200 MiB/s 250 MiB/s 250 MiB/s 250 MiB/s

If you notice high IO latency on some database file or you see that IOPS/throughput is reaching the limit, you might improve performance by increasing the file size.

There is also an instance-level limit on the max log write throughput (see the previous table for values, for example 22 MiB/s), so you may not be able to reach the max file throughout on the log file because you are hitting the instance throughput limit.

Supported regions

SQL Managed Instance can be created only in supported regions. To create a SQL Managed Instance in a region that is currently not supported, you can send a support request via the Azure portal.

Supported subscription types

SQL Managed Instance currently supports deployment only on the following types of subscriptions:

Regional resource limitations

Note

For the latest information on region availability for subscriptions, first check select a region.

Supported subscription types can contain a limited number of resources per region. SQL Managed Instance has two default limits per Azure region (that can be increased on-demand by creating a special support request in the Azure portal depending on a type of subscription type:

  • Subnet limit: The maximum number of subnets where instances of SQL Managed Instance are deployed in a single region.
  • vCore unit limit: The maximum number of vCore units that can be deployed across all instances in a single region. One GP vCore uses one vCore unit and one BC vCore takes four vCore units. The total number of instances is not limited as long as it is within the vCore unit limit.

Note

These limits are default settings and not technical limitations. The limits can be increased on-demand by creating a special support request in the Azure portal if you need more instances in the current region. As an alternative, you can create new instances of SQL Managed Instance in another Azure region without sending support requests.

The following table shows the default regional limits for supported subscription types (default limits can be extended using a support request):

Subscription type Default limit for SQL Managed Instance subnets Default limit for vCore units*
CSP 16 (30 in some regions**) 960 (1440 in some regions**)
EA 16 (30 in some regions**) 960 (1440 in some regions**)
Enterprise Dev/Test 6 320
Pay-as-you-go 6 320
Pay-as-you-go Dev/Test 6 320
Azure Pass 3 64
BizSpark 3 64
BizSpark Plus 3 64
Microsoft Azure Sponsorship 3 64
Microsoft Partner Network 3 64
Visual Studio Enterprise (MPN) 3 64
Visual Studio Enterprise 3 32
Visual Studio Enterprise (BizSpark) 3 32
Visual Studio Professional 3 32
MSDN Platforms 3 32

* In planning deployments, please take into consideration that Business Critical (BC) service tier requires four (4) times more vCore capacity than General Purpose (GP) service tier. For example: 1 GP vCore = 1 vCore unit and 1 BC vCore = 4 vCore. To simplify your consumption analysis against the default limits, summarize the vCore units across all subnets in the region where SQL Managed Instance is deployed and compare the results with the instance unit limits for your subscription type. Max number of vCore units limit applies to each subscription in a region. There is no limit per individual subnets except that the sum of all vCores deployed across multiple subnets must be lower or equal to max number of vCore units.

** Larger subnet and vCore limits are available in the following regions: Australia East, East US, East US 2, North Europe, South Central US, Southeast Asia, UK South, West Europe, West US 2.

Important

In case your vCore and subnet limit is 0, it means that default regional limit for your subscription type is not set. You can also use quota increase request for getting subscription access in specific region following the same procedure - providing required vCore and subnet values.

Request a quota increase

If you need more instances in your current regions, send a support request to extend the quota using the Azure portal. For more information, see Request quota increases for Azure SQL Database.

Next steps