How to choose between PSL4 and PSL5

Introduction

Storage type	Features	Use cases
PSL5 (PolarStore Level 5)	This storage class was used in earlier versions of PolarDB and is the default for clusters purchased before June 7, 2022. It offers higher performance, reliability, and availability.	Business-critical workloads that require high performance and reliability, such as finance, e-commerce, government services, and medium-to-large internet businesses.
PSL4 (PolarStore Level 4)	A new PolarDB storage class that uses Alibaba's proprietary smart-SSD technology. This technology compresses and decompresses data at the physical SSD layer, which reduces storage costs with a manageable performance impact.	Cost-sensitive applications that prioritize high cost-effectiveness.

Note

Storage class conversion rules:
- Some product series support upgrading the storage class from PSL4 to PSL5.
- Downgrading the storage class is not supported. You cannot downgrade PSL5 storage to PSL4 storage.
To switch from PSL5 storage to PSL4 storage, purchase a new cluster and migrate the data using either a migration tool like Data Transmission Service (DTS) or a major version upgrade.

Pricing

Subscription

Storage type		Price (USD/GB/month)
		Chinese mainland	Hong Kong (China) and other regions
PSL4	Dual-AZ with storage hot-standby cluster	0.2308	0.2569
	Dual-AZ with storage and compute hot-standby clusters
	Three-AZ with storage hot-standby cluster and logger nodes
	Single-AZ without storage hot-standby cluster	0.1154	0.1285
PSL5	Dual-AZ with storage hot-standby cluster	0.3492	0.3892
	Dual-AZ with storage and compute hot-standby clusters
	Three-AZ with storage hot-standby cluster and logger nodes
	Single-AZ without storage hot-standby cluster	0.1746	0.1946

Pay-as-you-go

Storage type		Price (USD/GB/hour)
		Chinese mainland	China (Hong Kong) and international
PSL4	Dual-AZ (storage hot-standby cluster enabled)	0.000486	0.000542
	Dual-AZ (storage hot-standby cluster and compute hot-standby cluster enabled)
	Triple-AZ (storage hot-standby cluster and logger node enabled)
	Single-AZ (storage hot-standby cluster disabled)	0.000243	0.000271
PSL5	Dual-AZ (storage hot-standby cluster enabled)	0.000748	0.000834
	Dual-AZ (storage hot-standby cluster and compute hot-standby cluster enabled)
	Triple-AZ (storage hot-standby cluster and logger node enabled)
	Single-AZ (storage hot-standby cluster disabled)	0.000374	0.000417

Serverless

Storage type		Price (USD/GB/hour)
		Regions in the Chinese mainland	China (Hong Kong) and regions outside China
PSL4	Dual-zone (hot standby storage cluster enabled)	0.000486	0.000542
	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	0.000271
PSL5	Dual-zone (hot standby storage cluster enabled)	0.000748	0.000834
	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	0.000417

Note

For PSL4 storage, a 4-core CPU is allocated for data compression for each terabyte (TB) of data. This CPU cost is included in the storage fee at no extra charge.

Data durability

Storage type	Data durability
PSL5	99.99999999%
PSL4	99.9999999%

Upgrade 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 or pay-as-you-go

Note
Serverless clusters do not support storage class upgrades.
Product version: Enterprise Edition
Product series: Cluster Edition
Storage class: PSL4

Procedure

Important

After you upgrade the storage class, the system calculates the related fees 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. Evaluate your requirements carefully before upgrading.

Log in to the PolarDB console. In the left-side navigation pane, click Clusters. Select the target cluster's region and click its ID to open the details page.
On the cluster details page, in the Distributed Storage section, click Storage Upgrade.

Performance metrics

For the same compute node specifications, PSL4 and PSL5 have the same maximum storage capacity and I/O bandwidth limit. However, their IOPS limits differ. For more information, see Enterprise Edition compute node specifications and Standard Edition compute node specifications.

Performance comparison

Tests on a dedicated cluster with 8 cores and 64 GB of memory measured the maximum queries per second (QPS) for several scenarios in an I/O-bound workload pattern to compare three backend storage options: Enterprise Edition PSL5, Enterprise Edition PSL4, and Standard Edition PL1 cloud disk. The data volume was approximately 800 GB to 1 TB. The following figure shows the test results.