Why shouldnt you remove your storage medium while working in an access database?

DB instances for Amazon RDS for MySQL, MariaDB, PostgreSQL, Oracle, and Microsoft SQL Server use Amazon Elastic Block Store (Amazon EBS) volumes for database and log storage. Depending on the amount of storage requested, Amazon RDS automatically stripes across multiple Amazon EBS volumes to enhance performance.

For more information about instance storage pricing, see Amazon RDS pricing.

Amazon RDS storage types

Amazon RDS provides three storage types: General Purpose SSD (also known as gp2 and gp3), Provisioned IOPS SSD (also known as io1), and magnetic (also known as standard). They differ in performance characteristics and price, which means that you can tailor your storage performance and cost to the needs of your database workload. You can create MySQL, MariaDB, Oracle, and PostgreSQL RDS DB instances with up to 64 tebibytes (TiB) of storage. You can create SQL Server RDS DB instances with up to 16 TiB of storage. For this amount of storage, use the Provisioned IOPS SSD and General Purpose SSD storage types.

The following list briefly describes the three storage types:

• General Purpose SSD – General Purpose SSD volumes offer cost-effective storage that is ideal for a broad range of workloads running on medium-sized DB instances. General Purpose storage is best suited for development and testing environments.

  For more information about General Purpose SSD storage, including the storage size ranges, see General Purpose SSD storage.

• Provisioned IOPS SSD – Provisioned IOPS storage is designed to meet the needs of I/O-intensive workloads, particularly database workloads, that require low I/O latency and consistent I/O throughput. Provisioned IOPS storage is best suited for production environments.

  For more information about Provisioned IOPS storage, including the storage size ranges, see Provisioned IOPS SSD storage.

• Magnetic – Amazon RDS also supports magnetic storage for backward compatibility. We recommend that you use General Purpose SSD or Provisioned IOPS SSD for any new storage needs. The maximum amount of storage allowed for DB instances on magnetic storage is less than that of the other storage types. For more information, see Magnetic storage.

General Purpose SSD storage

General Purpose SSD storage offers cost-effective storage that is acceptable for most database workloads that aren't latency sensitive. The following are the storage size ranges for General Purpose SSD DB instances:

• MariaDB, MySQL, Oracle, and PostgreSQL database instances: 20 GiB–64 TiB

• SQL Server Enterprise, Standard, Web, and Express Editions: 20 GiB–16 TiB

DB instances that use General Purpose SSD storage can experience much longer latency after read replica creation, Multi-AZ conversion, and DB snapshot restoration than instances that use Provisioned IOPS storage. If you need a DB instance with minimum latency after these operations, we recommend using Provisioned IOPS SSD storage.

Amazon RDS offers two types of General Purpose SSD storage: gp2 storage and gp3 storage.

gp2 storage

When your applications don't need high storage performance, you can use General Purpose SSD gp2 storage. Baseline I/O performance for gp2 storage is 3 IOPS for each GiB, with a minimum of 100 IOPS. This relationship means that larger volumes have better performance. For example, baseline performance for a 100-GiB volume is 300 IOPS. Baseline performance for a 1-TiB volume is 3,000 IOPS. Maximum baseline performance for a gp2 volume (5.34 TiB and greater) is 16,000 IOPS.

Volumes below 1 TiB in size also have the ability to burst to 3,000 IOPS for extended periods of time. Instance I/O credit balance determines burst performance. For more information about instance I/O credits, see I/O credits and burst performance in the Amazon EC2 User Guide. For a more detailed description of how baseline performance and I/O credit balance affect performance, see the post Understanding burst vs. baseline performance with Amazon RDS and gp2on the AWS Database Blog.

Many workloads never deplete the burst balance. However, some workloads can exhaust the 3,000 IOPS burst storage credit balance, so you should plan your storage capacity to meet the needs of your workloads.

For gp2 volumes larger than 1 TiB, the baseline performance is greater than the burst performance. For such volumes, burst is often irrelevant because the baseline performance is better than the 3,000 IOPS burst performance. However, for DB instances larger than 1 TiB where the storage is striped across four Amazon EBS volumes, burst performance of up to 12,000 IOPS can be seen. This applies to RDS database engines other than Microsoft SQL Server, which doesn't support volume striping.

gp3 storage

By using General Purpose SSD gp3 storage volumes, you can customize storage performance independently of storage capacity. Storage performance is the combination of I/O operations per second (IOPS) and how fast the storage volume can perform reads and writes (storage throughput). On gp3 storage volumes, Amazon RDS provides a baseline storage performance of 3000 IOPS and 125 MiBps.

For every RDS DB engine except RDS for SQL Server, when the storage size for gp3 volumes reaches a certain threshold, the baseline storage performance increases to 12,000 IOPS and 500 MiBps. This is because of volume striping, where the storage uses four logical volumes instead of one. RDS for SQL Server doesn't support volume striping, and therefore doesn't have a threshold value.

General Purpose SSD gp3 storage is supported on Single-AZ and Multi-AZ DB instances, but isn't supported on Multi-AZ DB clusters. For more information, see Multi-AZ deployments for high availability and Multi-AZ DB cluster deployments.

Storage performance for gp3 volumes on Amazon RDS DB engines, including the threshold, is shown in the following table.

DB engineStorage sizeBaseline storage performanceRange of Provisioned IOPSRange of provisioned storage throughputMariaDB, MySQL, and PostgreSQLLess than 400 GiB3,000 IOPS/125 MiBpsN/AN/AMariaDB, MySQL, and PostgreSQL400 GiB and higher12,000 IOPS/500 MiBps12,000–64,000 IOPS500–4,000 MiBpsOracleLess than 200 GiB3,000 IOPS/125 MiBpsN/AN/AOracle200 GiB and higher12,000 IOPS/500 MiBps12,000–64,000 IOPS500–4,000 MiBpsSQL Server20 GiB–16 TiB3,000 IOPS/125 MiBps3,000–16,000 IOPS125–1,000 MiBps

For every DB engine except RDS for SQL Server, you can provision additional IOPS and storage throughput when storage size is at or above the threshold value. For RDS for SQL Server, you can provision additional IOPS and storage throughput for any available storage size. For all DB engines, you pay for only the additional provisioned storage performance. For more information, see Amazon RDS pricing.

Although the added Provisioned IOPS and storage throughput aren't dependent on the storage size, they are related to each other. When you raise the IOPS above 32,000 for MariaDB and MySQL, the storage throughput value automatically increases from 500 MiBps. For example, when you set the IOPS to 40,000 on RDS for MySQL, the storage throughput must be at least 625 MiBps. The automatic increase doesn't happen for Oracle, PostgreSQL, and SQL Server DB instances.

Storage performance values for gp3 volumes on RDS have the following constraints:

• The maximum ratio of storage throughput to IOPS is 0.25 for all supported DB engines.

• The minimum ratio of IOPS to allocated storage (in GiB) is 0.5 on RDS for SQL Server. There is no minimum ratio for the other supported DB engines.

• The maximum ratio of IOPS to allocated storage is 500 for all supported DB engines.

• If you're using storage autoscaling, the same ratios between IOPS and maximum storage threshold (in GiB) also apply.

  For more information on storage autoscaling, see Managing capacity automatically with Amazon RDS storage autoscaling.

Provisioned IOPS SSD storage

For a production application that requires fast and consistent I/O performance, we recommend Provisioned IOPS (I/O operations per second) storage. Provisioned IOPS storage is a storage type that delivers predictable performance, and consistently low latency. Provisioned IOPS storage is optimized for online transaction processing (OLTP) workloads that have consistent performance requirements. Provisioned IOPS helps performance tuning of these workloads.

In some cases, your database workload might not be able to achieve 100 percent of the IOPS that you have provisioned. For more information, see Factors that affect storage performance.

When you create a DB instance, you specify the IOPS rate and the size of the volume. Amazon RDS provides that IOPS rate for the DB instance until you change it.

io1 storage

For I/O-intensive workloads, you can use Provisioned IOPS SSD io1 storage and achieve up to 256,000 I/O operations per second (IOPS). The following table shows the range of Provisioned IOPS and storage size for each database engine.

Database engineRange of Provisioned IOPSRange of storage sizeMariaDB1,000–256,000 IOPS100 GiB–64 TiBSQL Server1,000–64,000 IOPS20 GiB–16 TiBMySQL1,000–256,000 IOPS100 GiB–64 TiBOracle1,000–256,000 IOPS100 GiB–64 TiBPostgreSQL1,000–256,000 IOPS100 GiB–64 TiB

For SQL Server, the maximum 64,000 IOPS is guaranteed only on Nitro-based instances that are on the m5*, m6i, r5*, r6i, and z1d instance types. Other instance types guarantee performance up to 32,000 IOPS.

For Oracle, you can provision the maximum 256,000 IOPS only on the r5b instance type.

The IOPS and storage size ranges have the following constraints:

• The ratio of IOPS to allocated storage (in GiB) must be from 1–50 on RDS for SQL Server, and 0.5–50 on other RDS DB engines.

• If you're using storage autoscaling, the same ratios between IOPS and maximum storage threshold (in GiB) also apply.

  For more information on storage autoscaling, see Managing capacity automatically with Amazon RDS storage autoscaling.

Combining Provisioned IOPS storage with Multi-AZ deployments or read replicas

For production OLTP use cases, we recommend that you use Multi-AZ deployments for enhanced fault tolerance with Provisioned IOPS storage for fast and predictable performance.

You can also use Provisioned IOPS SSD storage with read replicas for MySQL, MariaDB or PostgreSQL. The type of storage for a read replica is independent of that on the primary DB instance. For example, you might use General Purpose SSD for read replicas with a primary DB instance that uses Provisioned IOPS SSD storage to reduce costs. However, your read replica's performance in this case might differ from that of a configuration where both the primary DB instance and the read replicas use Provisioned IOPS SSD storage.

Provisioned IOPS storage costs

With Provisioned IOPS storage, you are charged for the provisioned resources whether or not you use them in a given month.

For more information about pricing, see Amazon RDS pricing.

Getting the best performance from Amazon RDS Provisioned IOPS SSD storage

If your workload is I/O constrained, using Provisioned IOPS SSD storage can increase the number of I/O requests that the system can process concurrently. Increased concurrency allows for decreased latency because I/O requests spend less time in a queue. Decreased latency allows for faster database commits, which improves response time and allows for higher database throughput.

Provisioned IOPS SSD storage provides a way to reserve I/O capacity by specifying IOPS. However, as with any other system capacity attribute, its maximum throughput under load is constrained by the resource that is consumed first. That resource might be network bandwidth, CPU, memory, or database internal resources.

For more information about getting the most out of your Provisioned IOPS volumes, see Amazon EBS volume performance.

Comparing solid-state drive (SSD) storage types

The following table shows use cases and performance characteristics for the SSD storage volumes used by Amazon RDS.

CharacteristicProvisioned IOPS (io1)General Purpose (gp3)General Purpose (gp2)Description

Consistent storage performance (IOPS, throughput, latency)

Designed for latency-sensitive, transactional workloads.

Flexibility in provisioning storage, IOPS, and throughput independently

Balances price performance for a wide variety of transactional workloads

Provides burstable IOPS

Balances price performance for a wide variety of transactional workloads

Use cases

Transactional workloads that require sustained IOPS performance up to 256,000 IOPS

Broad range of workloads running on medium-sized relational databases in development/test environments

Broad range of workloads running on medium-sized relational databases in development/test environments

Latency

Single-digit millisecond, provided consistently 99.9% of the time

Single-digit millisecond, provided consistently 99% of the time

Single-digit millisecond, provided consistently 99% of the time

Volume size

100 GiB–64 TiB (16 TiB on RDS for SQL Server)

20 GiB–64 TiB (16 TiB on RDS for SQL Server)

20 GiB–64 TiB (16 TiB on RDS for SQL Server)

Maximum IOPS256,000 (64,000 on RDS for SQL Server)64,000 (16,000 on RDS for SQL Server)16,000Maximum throughputScales based on Provisioned IOPS up to 4,000 MB/sProvision additional throughput up to 4,000 MB/s1000 MB/s (250 MB/s on RDS for SQL Server)AWS CLI and RDS API nameio1gp3gp2

Magnetic storage

Amazon RDS also supports magnetic storage for backward compatibility. We recommend that you use General Purpose SSD or Provisioned IOPS SSD for any new storage needs. The following are some limitations for magnetic storage:

• Doesn't allow you to scale storage when using the SQL Server database engine.

• Doesn't support storage autoscaling.

• Doesn't support elastic volumes.

• Limited to a maximum size of 3 TiB.

• Limited to a maximum of 1,000 IOPS.

Monitoring storage performance

Amazon RDS provides several metrics that you can use to determine how your DB instance is performing. You can view the metrics on the summary page for your instance in Amazon RDS Management Console. You can also use Amazon CloudWatch to monitor these metrics. For more information, see Viewing metrics in the Amazon RDS console. Enhanced Monitoring provides more detailed I/O metrics; for more information, see Monitoring OS metrics with Enhanced Monitoring.

The following metrics are useful for monitoring storage for your DB instance:

• IOPS – The number of I/O operations completed each second. This metric is reported as the average IOPS for a given time interval. Amazon RDS reports read and write IOPS separately on 1-minute intervals. Total IOPS is the sum of the read and write IOPS. Typical values for IOPS range from zero to tens of thousands per second.

• Latency – The elapsed time between the submission of an I/O request and its completion. This metric is reported as the average latency for a given time interval. Amazon RDS reports read and write latency separately at 1-minute intervals. Typical values for latency are in milliseconds (ms).

• Throughput – The number of bytes each second that are transferred to or from disk. This metric is reported as the average throughput for a given time interval. Amazon RDS reports read and write throughput separately on 1-minute intervals using units of megabytes per second (MB/s). Typical values for throughput range from zero to the I/O channel's maximum bandwidth.

• Queue Depth – The number of I/O requests in the queue waiting to be serviced. These are I/O requests that have been submitted by the application but have not been sent to the device because the device is busy servicing other I/O requests. Time spent waiting in the queue is a component of latency and service time (not available as a metric). This metric is reported as the average queue depth for a given time interval. Amazon RDS reports queue depth in 1-minute intervals. Typical values for queue depth range from zero to several hundred.

Measured IOPS values are independent of the size of the individual I/O operation. This means that when you measure I/O performance, make sure to look at the throughput of the instance, not simply the number of I/O operations.

Factors that affect storage performance

System activities, database workload, and DB instance class can affect storage performance.

System activities

The following system-related activities consume I/O capacity and might reduce DB instance performance while in progress:

• Multi-AZ standby creation

• Read replica creation

• Changing storage types

Database workload

In some cases, your database or application design results in concurrency issues, locking, or other forms of database contention. In these cases, you might not be able to use all the provisioned bandwidth directly. In addition, you might encounter the following workload-related situations:

• The throughput limit of the underlying instance type is reached.

• Queue depth is consistently less than 1 because your application isn't driving enough I/O operations.

• You experience query contention in the database even though some I/O capacity is unused.

In some cases, there isn't a system resource that is at or near a limit, and adding threads doesn't increase the database transaction rate. In such cases, the bottleneck is most likely contention in the database. The most common forms are row lock and index page lock contention, but there are many other possibilities. If this is your situation, seek the advice of a database performance tuning expert.

DB instance class

To get the most performance out of your Amazon RDS DB instance, choose a current generation instance type with enough bandwidth to support your storage type. For example, you can choose Amazon EBS–optimized instances and instances with 10-gigabit network connectivity.

Depending on the instance class you're using, you might see lower IOPS performance than the maximum that you can provision with RDS. For specific information on IOPS performance for DB instance classes, see Amazon EBS–optimized instances in the Amazon EC2 User Guide. We recommend that you determine the maximum IOPS for the instance class before setting a Provisioned IOPS value for your DB instance.

We encourage you to use the latest generation of instances to get the best performance. Previous generation DB instances can also have lower maximum storage.

Some older 32-bit file systems might have lower storage capacities. To determine the storage capacity of your DB instance, you can use the describe-valid-db-instance-modifications AWS CLI command.

The following list shows the maximum storage that most DB instance classes can scale to for each database engine:

• MariaDB – 64 TiB

• Microsoft SQL Server – 16 TiB

• MySQL – 64 TiB

• Oracle – 64 TiB

• PostgreSQL – 64 TiB

The following table shows some exceptions for maximum storage (in TiB). All RDS for Microsoft SQL Server DB instances have a maximum storage of 16 TiB, so there are no entries for SQL Server.

Instance classMariaDBMySQLOraclePostgreSQLdb.m3 – standard instance classesdb.m3.2xlargeN/A6N/A6db.m3.xlargeN/A6N/A6db.m3.largeN/A6N/A6db.m3.mediumN/A32N/A32db.t4g – burstable-performance instance classesdb.t4g.medium1616N/A32db.t4g.small1616N/A16db.t4g.micro66N/A6db.t3 – burstable-performance instance classesdb.t3.medium16163232db.t3.small16163216db.t3.micro66326db.t2 – burstable-performance instance classesdb.t2.medium3232N/A32db.t2.small1616N/A16db.t2.micro66N/A6

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