Cloud disks are block-level data storage products provided by Alibaba Cloud for ECS. They feature low latency and high durability and reliability.

Cloud disks provided by Alibaba Cloud support data redundancy through the replication of data three times by default, and the storage of the data copies across different servers, to provide 99.9999999% data reliability for ECS instances. This means that if service disruptions occur (for example, due to hardware failure), data within the target zone is copied to an unaffected cloud disk to help ensure data availability. You can partition and format cloud disks attached to an ECS instance, and create a file system and store data on the cloud disk. For more information, see Triplicate technology.

Note You can only attach a cloud disk to one ECS instance that is in the same zone of the same region as the cloud disk.

Cloud disk types

The following tables classify cloud disk types by performance and function.

  • By performance

    Type Description
    ESSD cloud disk An Enhanced SSD (ESSD) cloud disk is an ultra-high performance cloud disk provided by Alibaba Cloud. ESSD cloud disks are based on the next-generation distributed block storage architecture, a 25GE network, and remote direct memory access (RDMA) technology. They deliver a maximum random IOPS of 1 million per disk and low latency. For more information, see Block storage FAQ.
    SSD cloud disk High-performance disks with stable and high random I/O performance, and high data reliability.
    Ultra cloud disk Cloud disks with high cost performance, medium random I/O performance, and high data reliability.
    Basic cloud disk Cloud disks with high data reliability and standard random I/O performance.

  • By function

    Type Description
    System disk A system disk has the same life cycle as the ECS instance to which it is mounted, and is created and released along with the ECS instance. Shared access to the system disk is not allowed. The available size of a system disk varies according to the operating system as follows:
    • Linux (excluding CoreOS) and FreeBSD: 20−500 GiB
    • CoreOS: 30−500 GiB
    • Windows: 40−500 GiB
    Data disk Data disks can be created separately or at the same time as ECS instances.
    • Data disks created along with ECS instances have the same life cycle as the corresponding instance, and are released along with the instance.
    • Data disks created separately can be released separately or at the same time as the corresponding ECS instance.
    Shared access to a data disk is not allowed. The performance of data disks depends on the cloud disk type. For more information, see Block storage performance.
    Note When used as data disks, up to 16 cloud disks can be attached to one ECS instance.

Performance

For the performance of each type of cloud disk, see Block storage performance.

Billing method

  • Cloud disks created along with Subscription instances or created separately for Subscription instances are billed according to the selected billing cycle and are charged before you use the service. For more information, see Subscription.
  • Cloud disks created separately or created along with Pay-As-You-Go instances are billed based on the amount of resources you actually use. For more information, see Pay-As-You-Go.

You can change the billing method of a cloud disk, as described in the following table.

Conversion of billing methods Related Feature Effective time Suitable for
From Subscription to Pay-As-You-Go Renew for configuration downgrade Effective from the next billing cycle Subscription cloud disks mounted to Subscription instances. The billing method of the system disk cannot be changed.
Switch from Subscription to Pay-As-You-Go billing Effective immediately The system disk of Subscription instances and data disks created along with Subscription instances.
From Pay-As-You-Go to Subscription Upgrade configurations Effective immediately Pay-As-You-Go data disks mounted to Subscription instances. The billing method of the system disk cannot be changed.
Switch from Pay-As-You-Go to Subscription billing System disks and data disks mounted to Pay-As-You-Go instances.

Related operations

You can perform the following operations on a cloud disk:
Note Some of the following operations are dependent on whether the cloud disk functions as a system disk or a data disk.