PolarDB offers two storage classes for different business scenarios: PSL4 and PSL5. The two storage classes differ in price, data reliability, and performance. This topic describes the differences between them to help you make an informed decision.
Introduction
Storage class | Features | Scenarios |
PSL5 (PolarStore Level 5) | A storage class supported in earlier versions of PolarDB. It is the default storage class for PolarDB clusters purchased before June 7, 2022. It provides better performance, reliability, and availability. | Business scenarios that require high performance and reliability, where the database is a core system. Such scenarios include finance, e-commerce, government services, and medium-to-large Internet businesses. |
PSL4 (PolarStore Level 4) | PolarDB launched this new storage class that uses Alibaba's proprietary smart-SSD technology. This technology compresses and decompresses data at the physical SSD disk layer. This lowers the storage price per unit of data while keeping the performance impact under control. | Application scenarios that require cost reduction and high cost-effectiveness. |
Storage class conversion rules:
Some product series support storage class upgrades, which means that PSL4 storage can be upgraded to PSL5 storage.
Downgrading the storage class is not supported. You cannot downgrade PSL5 storage to PSL4 storage.
To switch from PSL5 storage to PSL4 storage, you can purchase a new cluster and migrate the data from the original cluster to the new cluster using a migration tool such as DTS or the major version upgrade feature.
Price
Subscription
Storage class | Price (USD/GB/month) | ||
The Chinese mainland | China (Hong Kong) and other regions | ||
PSL4 | Dual-zone deployment (hot standby storage cluster enabled) | 0.2308 | 0.2569 |
Dual-zone deployment (hot standby storage and compute clusters enabled) | |||
Three-zone deployment (hot standby storage cluster and logger node enabled) | |||
Single zone (hot standby storage cluster disabled) | 0.1154 | 0.1285 | |
PSL5 | Dual-zone deployment (hot standby storage cluster enabled) | 0.3492 | 0.3892 |
Dual-zone deployment (hot standby storage and compute clusters enabled) | |||
Three-zone deployment (hot standby storage cluster and logger node enabled) | |||
Single zone (hot standby storage cluster disabled) | 0.1746 | 0.1946 | |
Pay-as-you-go
Storage class | Price (USD/GB/hour) | ||
The Chinese mainland | China (Hong Kong) and other regions | ||
PSL4 | Dual-zone deployment (hot standby storage cluster enabled) | 0.000486 | 0.000542 |
Dual-zone deployment (hot standby storage and compute clusters enabled) | |||
Three-zone deployment (hot standby storage cluster and logger node enabled) | |||
Single zone (hot standby storage cluster disabled) | 0.000243 | 0.000271 | |
PSL5 | Dual-zone deployment (hot standby storage cluster enabled) | 0.000748 | 0.000834 |
Dual-zone deployment (hot standby storage and compute clusters enabled) | |||
Three-zone deployment (hot standby storage cluster and logger node enabled) | |||
Single zone (hot standby storage cluster disabled) | 0.000374 | 0.000417 | |
Serverless
Storage type | Price (USD per GB-hour) | |||
Regions in the Chinese mainland | China (Hong Kong) and regions outside China | |||
PSL4 | Dual-zone (hot standby storage cluster enabled) | 0.0004860 | 0.000486 | |
Dual-zone (hot standby storage cluster and compute cluster enabled) | ||||
Three-zone (hot standby storage cluster and logger node enabled) | ||||
Single-zone (hot standby storage cluster disabled) | 0.000243 | 0.000243 | ||
PSL5 | Dual-zone (hot standby storage cluster enabled) | 0.000748 | 0.000748 | |
Dual-zone (hot standby storage cluster and compute cluster enabled) | ||||
Three-zone (hot standby storage cluster and logger node enabled) | ||||
Single-zone (hot standby storage cluster disabled) | 0.000374 | 0.000374 | ||
For PSL4 storage, a 4-core CPU is allocated for data compression for each TB of data. The cost of this CPU is included in the storage fee, and no extra charges are incurred.
Data reliability
Storage class | Data durability |
PSL5 | 99.99999999% |
PSL4 | 99.9999999% |
Upgrade the storage class
If PSL4 storage no longer meets your business requirements, you can manually upgrade it to PSL5 storage in the PolarDB console.
Prerequisites
Your PolarDB for MySQL cluster must meet the following requirements:
Billing method: Subscription and pay-as-you-go
NoteServerless clusters do not support storage class upgrades.
Edition: Enterprise Edition
Product series: Cluster Edition
Storage class: PSL4
Procedure
After you upgrade the storage class, the related fees are calculated based on the billing method for the cluster's storage. For more information, see Billing of configuration changes.
The storage class cannot be downgraded from PSL5 to PSL4. Carefully evaluate your requirements before you perform the upgrade.
Log on to the PolarDB console. In the navigation pane on the left, click Cluster List. Select the region of the target cluster and click its ID to open the Cluster Details page.
On the Cluster Details page, in the Database Distributed Storage section, click Upgrade Storage Class.
Performance metrics
For the same compute node specifications, PSL4 and PSL5 have the same maximum storage capacity and I/O bandwidth limit. However, their input/output operations per second (IOPS) limits are different. For more information, see Enterprise Edition compute node specifications and Standard Edition compute node specifications.
Performance comparison
A test was run on a Dedicated cluster with 8 cores and 64 GB of memory. The backend storage options tested were Enterprise Edition PSL5, Enterprise Edition PSL4, and Standard Edition PL1 disks. The test measured the maximum queries per second (QPS) for several scenarios in the IOBOUND payload pattern. The data volume was approximately 800 GB to 1 TB. The following figure shows the test results.
