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# Storage Capacity Unit:Offset rules for EBS

Last Updated:Jul 20, 2023

Storage capacity units (SCUs) are subscription storage resource plans that can be used to offset the pay-as-you-go bills of various storage resources. Compared with disks purchased together with subscription Elastic Compute Service (ECS) instances or resource plans of a specific resource, SCUs offer a better combination of cost-effectiveness and flexibility together with pay-as-you-go resources.

## Offset rules

SCUs can be used to offset the storage fees of multiple Alibaba Cloud storage services. The following table describes the rules that apply when you use SCUs to offset the storage fees of different cloud disk resources in regions in the Chinese mainland.

Note

For more information about the rules that apply to other Alibaba Cloud storage services and regions, visit the pricing page.

 Type Offset factor Description Ultra disk 1 Each GiB of PL1 ultra disk space consumes 1 GiB of an SCU. Standard SSD 1 Each GiB of standard SSD space consumes 1 GiB of an SCU. PL0 enhanced SSD (ESSD) 0.5 Each GiB of PL0 ESSD space consumes 0.5 GiB of an SCU. PL1 ESSD 1 Each GiB of PL1 ESSD space consumes 1 GiB of an SCU. PL2 ESSD 2 Each GiB of PL2 ESSD space consumes 2 GiB of an SCU. PL3 ESSD 4 Each GiB of PL3 ESSD space consumes 4 GiB of an SCU.

## Examples

If you purchase a 10 TiB SCU and use only cloud disk resources, the SCU can be applied to a combination of different types of storage resources. The following examples show the possible offset combinations:

• Method 1

The SCU is used to offset the bills for the following item: 10 TiB of PL1 ESSDs. Capacity of the SCU = 10 TiB x 1. In this case, 10 TiB of SCU is consumed.

• Method 2

The SCU is used to offset the bills for the following items: 10 TiB of PL0 ESSDs and 5 TiB of PL1 ESSDs. Capacity of the SCU = 10 TiB x 0.5 + 5 TiB x1. In this case, 10 TiB of SCU is consumed.

• Method 3

The SCU is used to offset the bills for the following items: 1 TiB of PL3 ESSDs, 2 TiB of PL2 ESSDs, and 2 TiB of PL1 ESSDs. Capacity of the SCU = 1 TiB x 4 + 2 TiB x 2 + 2 TiB x 1. In this case, 10 TiB of SCU is consumed.

• Method 4

The SCU is used to offset the bills for the following item: 12 TiB of standard SSDs. In this case, 10 TiB of SCU is consumed and you are charged for the remaining 2 TiB on a pay-as-you-go basis.