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.

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.

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)	4-80 vCores	4-80 vCores	4-64 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 storage1	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 Dependent on the number of vCores.

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:

China North 3

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
8 vCores	6.28 GB	8.79 GB	22.06 GB
16 vCores	15.77 GB	22.06 GB	57.58 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
64 vCores	99.9 GB	139.82 GB	288.61 GB
80 vCores	131.68 GB	184.30 GB

Service tier characteristics

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

Number of vCores

Hardware Generation	General Purpose	Business Critical
Standard-series (Gen5)	21, 4, 8, 16, 24, 32, 40, 64, 80	4, 8, 16, 24, 32, 40, 64, 80
Premium-series	4, 8, 16, 24, 32, 40, 64, 80	4, 8, 16, 24, 32, 40, 64, 80
Memory optimized premium-series	4, 8, 16, 24, 32, 40, 64	4, 8, 16, 24, 32, 40, 64

Max memory

Hardware Generation	General Purpose	Business Critical
Standard-series (Gen5)	20.4 GB - 408 GB 5.1 GB/vCore	20.4 GB - 408 GB 5.1 GB/vCore on each replica
Premium-series	28 GB - 560 GB 7 GB/vCore	28 GB - 560 GB 7 GB/vCore up to 80 vCores on each replica
Memory optimized premium-series	54.4 GB - 870.4 GB 13.6 GB/vCore	54.4 GB - 870.4 GB 13.6 GB/vCore up to 64 vCores on each replica

Max instance storage size (reserved)

Hardware Generation	General Purpose	Business Critical
Standard-series (Gen5)	- 2 TB for 4 vCores - 8 TB for 8 vCores - 16 TB for other sizes	- 1 TB for 4, 8, 16 vCores - 2 TB for 24 vCores - 4 TB for 32, 40, 64, 80 vCores
Premium-series	- 2 TB for 4 vCores - 8 TB for 8 vCores - 16 TB for other sizes	- 1 TB for 4, 8 vCores - 2 TB for 16, 24 vCores - 4 TB for 32 vCores - 5.5 TB for 40, 64, 80 vCores
Memory optimized premium-series	- 2 TB for 4 vCores - 8 TB for 8 vCores - 16 TB for other sizes	- 1 TB for 4, 8 vCores - 2 TB for 16, 24 vCores - 4 TB for 32 vCores - 5.5 TB for 40 vCores - 16 TB for 64 vCores

Feature comparison

Feature	General Purpose	Business Critical
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.
Data throughput (approximate)	100 - 250 MiB/s per file *Increase the file size to get better IO performance	Not limited.
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
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 vCores
Replicas for availability	Stand by nodes for high availability	Four high availability replicas, 1 is also a read-scale replica
Read-only replicas with failover groups enabled	One additional read-only replica. Two total readable replicas, which include the primary replica.	Two additional read-only replicas, three total read-only replicas. Four total readable replicas, which include the primary replica.
Pricing/billing	vCore, reserved storage, and backup storage is charged. IOPS are not charged	vCore, reserved storage, and backup storage is charged. IOPS are not charged.
Discount models	Azure Hybrid Benefit (not available on dev/test subscriptions) Enterprise and pay-as-you-go Dev/Test subscriptions	Azure Hybrid Benefit (not available on dev/test subscriptions) Enterprise and pay-as-you-go Dev/Test subscriptions

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 aren't persisted and not included in the size. Backups aren't included in storage size.
• Throughput and IOPS in the General Purpose tier also depends on the file size, and isn't explicitly limited by the SQL Managed Instance.
• 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 autobackups.
• You can create another readable replica in a different Azure region using failover groups
• Names of tempdbfiles can't have more than 16 characters.

IOPS

For the Business Critical service tiers, available IOPS are dictated by the number of vCores: Business Critical service tier: uses a formula (4000 IOPS/vCore) to determine IOPS limits.

The following table lists the max IOPS available based on the number of vCores:

Number of vCores	Business Critical
4	16,000
8	32,000
16	64,000
24	96,000
32	128,000
40	160,000
64	256,000
80	320,000

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

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.

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.

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 is used for LTR backups. For more information, see Long-term backup retention.

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.

Regional resource limitations

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 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 isn't limited as long as it is within the vCore unit limit.

Next steps

• For more information about SQL Managed Instance, see What is a SQL Managed Instance?.
• For pricing information, see SQL Managed Instance pricing.
• To learn how to create your first SQL Managed Instance, see the quickstart guide.