PolarDB for PostgreSQL (Compatible with Oracle) offers two storage types: PSL4 (PolarStore Level 4) and PSL5 (PolarStore Level 5). PSL5 provides higher performance and data durability; PSL4 reduces storage costs through hardware-level compression. Use this page to compare their capabilities and identify which type fits your workload.
Storage type comparison
| PSL5 | PSL4 | |
|---|---|---|
| Full name | PolarStore Level 5 | PolarStore Level 4 |
| Technology | Standard PolarStore storage | Alibaba Cloud smart-SSD — compresses and decompresses data at the physical SSD level |
| Data durability | 99.99999999% | 99.9999999% |
| Max storage capacity | Same as PSL4 (varies by node spec) | Same as PSL5 (varies by node spec) |
| I/O bandwidth | Same as PSL4 (varies by node spec) | Same as PSL5 (varies by node spec) |
| Max IOPS | Higher (see ) | Lower than PSL5 (see ) |
| Typical use cases | I/O-intensive workloads: finance, e-commerce, government, and large- to medium-sized internet services | Cost-sensitive workloads where storage spend is the priority |
| Default for clusters purchased before June 7, 2022 | Yes | No |
Choose a storage type
Use the following criteria to decide:
Choose PSL5 if your workload is I/O-intensive and consistent throughput matters more than storage cost — for example, online transaction processing (OLTP) systems, core financial databases, or high-traffic e-commerce platforms where IOPS limits directly affect response times.
Choose PSL4 if reducing storage costs is the primary goal and your workload tolerates lower IOPS limits — for example, development and test environments, archival workloads, or applications with moderate and predictable I/O patterns.
If you are unsure, start with PSL4. You can upgrade to PSL5 later if performance requirements increase. Downgrading from PSL5 to PSL4 is not supported.
Before you purchase, factor in the switching constraints. Upgrading from PSL4 to PSL5 is supported but downgrading is not. If you choose PSL5 and later want PSL4, you must purchase a new cluster and migrate your data.
Storage pricing
Chinese mainland
| Storage type | Configuration | 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 |
| 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 | |
| PSL4 | Dual-zone (hot standby storage cluster enabled) | USD 0.000486 per GB-hour | USD 0.231 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 |
China (Hong Kong) and other regions
| Storage type | Configuration | Pay-by-capacity (pay-as-you-go) | Pay-by-space (subscription) |
|---|---|---|---|
| PSL5 | Dual-zone (hot standby storage cluster enabled) | 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 0.000417 per GB/hour | USD 0.195 per GB-month | |
| PSL4 | Dual-zone (hot standby storage cluster enabled) | 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 0.000271 per GB/hour | USD 0.129 per GB-month |
PSL4 dual-zone storage costs approximately 35% less than PSL5 dual-zone storage in the Chinese mainland region.
Performance comparison
PSL4 and PSL5 share the same maximum storage capacity and I/O bandwidth for equivalent node specifications. The key difference is the maximum IOPS limit, which is higher on PSL5. For exact IOPS values per node spec, see .
The following figure shows maximum QPS results from an IOBOUND load test on a dedicated cluster with 8 cores, 64 GB memory, and approximately 900 GB of data.
Switching storage types
Storage type changes are one-directional:
| Direction | Supported | Notes |
|---|---|---|
| PSL4 to PSL5 | Yes | Upgrade in the PolarDB console if the cluster meets eligibility requirements |
| PSL5 to PSL4 | No | Purchase a new PSL4 cluster and migrate your data |
Upgrade from PSL4 to PSL5
Eligibility
The cluster must meet all of the following conditions:
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Billing method: Subscription or pay-as-you-go (Serverless clusters are not supported)
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Edition: Enterprise Edition
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Product series: Cluster Edition
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Storage type: PSL4
Upgrade procedure
After the upgrade, storage fees are calculated based on your cluster's billing method. For details, see Billing of configuration changes. Downgrading from PSL5 to PSL4 is not supported — evaluate the upgrade before proceeding.
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Log on to the PolarDB console. In the left navigation pane, click Clusters.
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Select the region where your cluster is located, then click the cluster ID to go to the details page.
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In the Distributed Storage section, click Storage Upgrade.
