PolarDB for PostgreSQL (Compatible with Oracle) supports two storage types: PSL4 and PSL5. This topic describes the differences between these two storage types to help you select the appropriate one.
Overview of storage types
Storage type | Features | Scenarios |
PSL5 (PolarStore Level 5) | This is the storage type supported in earlier versions of PolarDB. It is the default storage type for PolarDB clusters purchased before June 7, 2022. It provides high performance, reliability, and availability. | Business scenarios that require high performance and reliability and use databases as core systems, such as finance, e-commerce, government affairs, and large- and medium-sized internet services. |
PSL4 (PolarStore Level 4) | PolarDB introduces this new storage type that uses Alibaba Cloud's proprietary smart-SSD technology. This technology compresses and decompresses data at the physical solid-state drive (SSD) level. This lowers the storage price per unit of data while keeping the performance impact manageable. | Application scenarios that require cost reduction and high cost-effectiveness. |
You cannot change the storage type of an existing cluster. To switch the storage type, you must purchase a new cluster with the desired storage type and then migrate the data from the original cluster to the new one.
Storage pricing
Storage type | Chinese mainland | China (Hong Kong) and other regions | |||
Pay-by-capacity (pay-as-you-go) | Pay-by-space (subscription) | Pay-by-capacity (pay-as-you-go) | Pay-by-space (subscription) | ||
PSL5 | Dual-zone (hot standby storage cluster enabled) | USD 0.000748 per GB-hour | USD 0.349 per GB-month | USD 0.000834 per GB/hour | USD 0.389 per GB-month |
Dual-zone (hot standby storage cluster and compute standby enabled) | |||||
Single-zone (hot standby storage cluster disabled) | USD 0.000374 per GB-hour | USD 0.175 per GB-month | USD 0.000417 per GB/hour | USD 0.195 per GB-month | |
PSL4 | Dual-zone (hot standby storage cluster enabled) | USD 0.000486 per GB-hour | USD 0.231 per GB-month | USD 0.000542 per GB/hour | USD 0.257 per GB-month |
Dual-zone (hot standby storage cluster and compute standby enabled) | |||||
Single-zone (hot standby storage cluster disabled) | USD 0.000243 per GB-hour | USD 0.115 per GB-month | USD 0.000271 per GB/hour | USD 0.129 per GB-month | |
Data reliability
Storage type | Data durability |
PSL5 | 99.99999999% |
PSL4 | 99.9999999% |
Upgrade the storage type
If PSL4 storage cannot meet your business needs, you can manually upgrade it to PSL5 in the PolarDB console.
Applicability
The cluster must meet the following conditions:
Billing method: Subscription and pay-as-you-go
NoteServerless clusters do not support storage type upgrades.
Edition: Enterprise Edition
Product series: Cluster Edition
Storage type: PSL4
Procedure
After you upgrade the storage type, fees are calculated based on the billing method of the cluster storage. For more information, see Billing of configuration changes.
You cannot downgrade the storage type from PSL5 to PSL4. Carefully evaluate the upgrade before you proceed.
Log on to the PolarDB console. In the navigation pane on the left, click Clusters. Select the region where your cluster is located, and then click the cluster ID to go to the details page.
In the Distributed Storage section of the cluster details page, click Storage Upgrade.
Performance metrics
For the same node specifications, PSL4 and PSL5 have the same maximum storage capacity and I/O bandwidth limit. However, they have different maximum input/output operations per second (IOPS) limits. For more information, see Compute node specifications.
Performance comparison
The maximum QPS was tested in IOBOUND load mode for several scenarios. The test was performed on a dedicated cluster with 8 cores, 64 GB of memory, and approximately 900 GB of data. The backend storage options tested were PSL5 and PSL4. The results are shown in the following figure.
