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PolarDB:Comparison between PSL4 and PSL5

Last Updated:Nov 15, 2023

PolarDB for MySQL provides two storage types: PolarStore Level 4 (PSL4) and PolarStore Level 5 (PSL5). This topic compares the two storage types to assist your selection.

Storage types

Storage type




This is the storage type supported by historical versions of PolarDB and the default storage type for PolarDB clusters purchased before June 7, 2022. It delivers higher performance, reliability and availability. This storage type is also called PSL5.

Databases are the key component of business systems that require high reliability, such as finance, e-commerce, public service sectors, and medium- or large-scale Internet services.


PSL4 is supported for PolarDB. PSL4 uses the Smart-SSD technology developed in-house by Alibaba Cloud to compress and decompress data at the physical SSD disk level. This reduces the storage costs of data and ensures high disk performance.

Cost-effectiveness is prioritized.


The storage type of existing clusters cannot be changed to PSL4. To change the storage type, we recommend that you purchase a new cluster, configure the desired storage type, and then migrate data from the original cluster to the new cluster by using an external migration tool (such as DTS) or the one-click upgrade feature of PolarDB. For more information, see Major version upgrades.


Storage type

Region in the Chinese mainland

Region outside the Chinese mainland






USD 0.00077 per GB-hour

USD 0.365 per GB-month

USD 0.00085 per GB-hour

USD 0.403 per GB-month


USD 0.0005 per GB-hour

USD 0.238 per GB-month

USD 0.000552 per GB-hour

USD 0.263 per GB-month


For PSL4, four CPU cores are allocated for compressing 1 TB of data. The CPU costs are already included in the storage fees and no additional charges are required.

Data reliability

Storage type

Data durability





Maximum IOPS and capacity

For the same node specifications, PSL4 provides half the maximum IOPS of PSL5 and the same maximum capacity as PSL5. For more information, see Compute node specifications of PolarDB for MySQL Enterprise Edition.


The test on the maximum QPS of a dedicated cluster that uses the specifications of 8 cores and 32 GB of memory shows that the performance difference between PSL4 and PSL5 in IOBOUND load modes is generally within 10%.

  • The performance of PSL4 is slightly lower than that of PSL5 in oltp_insert, oltp_point_select, oltp_read_only, and oltp_read_write load modes.

  • The performance of PSL4 is slightly higher than that of PSL5 in oltp_update_index, oltp_update_non_index, and oltp_write_only load modes.