Disks are block-level data storage products provided by Alibaba Cloud for ECS. They feature low latency and high performance, durability, and reliability. Disks use a distributed triplicate mechanism to ensure 99.9999999% data durability for ECS instances. If service disruptions occur (for example, due to hardware failure) within a zone, data in that zone is copied to an unaffected disk in another zone to ensure data availability.

Disk categories

As with hard disks, you can partition and format cloud disks that are attached to ECS instances, and create file systems and persistently store data on the cloud disks. The following table lists the disk categories by performance.

Category Description
Enhanced SSD (ESSD) ESSDs are based on the next-generation distributed block storage architecture and the 25 Gigabit Ethernet (25 GE) and remote direct memory access (RDMA) technologies. Each ESSD has low latency and can deliver up to one million IOPS. For more information, see Enhanced SSDs.
Standard SSD Standard SSDs are high-performance disks that feature consistent and high random IOPS performance and high data reliability.
Ultra disk Ultra disks feature high cost-effectiveness, medium random IOPS performance, and high data reliability.
Basic disk Basic disks feature high data reliability and standard random IOPS performance.

Disk types

A disk can be used as a system disk or a data disk based on the type of stored data and the creation method of the disk.

Type Description Notes Maximum number of disks per instance Disk size
Disk capacity Shared access to a system disk is not allowed. When a system disk is initialized, the image based on which the system disk was created determines the operating system type and application data. Only cloud disks can be used as system disks. Cannot be created separately. A system disk must be created with an instance and shares the same lifecycle as the instance. 1 The minimum size of a system disk depends on the image based on which the system disk was created. The actual size is displayed on the instance buy page.
  • Windows Server: 40 GiB to 500 GiB
  • CoreOS and FreeBSD: 30 GiB to 500 GiB
  • Linux systems excluding CoreOS: 20 GiB to 500 GiB
Data disk A data disk is used to store application data. It can be created separately or together with an ECS instance. Cloud disks or Block Storage devices of other types such as local disks can be used as data disks. For more information, see Local disks. Can be created separately. 16 Up to 32 TiB. For more information, see Block Storage performance.
Note When a disk is created, the disk capacity displayed in the ECS console includes the capacity occupied by the system, and the remaining available capacity may be less than the disk capacity displayed in the ECS console. For example, if the capacity of a system disk displayed in the ECS console is 40 GiB, the remaining available capacity may be less than 40 GiB because the operating system occupies some of the disk capacity.

Limits

A disk can be attached to only one ECS instance in the same zone.

For more information, see the "Block Storage limits" section in Limits.

Billing methods

Disks can be billed on a subscription or a pay-as-you-go basis. For more information, see Subscription and Pay-as-you-go.

  • Disks that are created with subscription instances or created separately for subscription instances are billed on a subscription basis.
  • Disks that are created with pay-as-you-go instances or created separately for pay-as-you-go instances are billed on a pay-as-you-go basis. Storage capacity units (SCUs) can be used to offset the bills of pay-as-you-go disks.

After a disk is created, you can change its billing method. For more information, see Convert the billing method of a cloud disk.

Related operations

You can perform the following operations on a disk:

Operation Reference
Attach an idle pay-as-you-go disk to an ECS instance
  1. Attach a data disk
  2. Format the data disk based on the operating system:
Create a subscription data disk
  1. Create a subscription disk
  2. Format the data disk based on the operating system:
Create a data disk separately
  1. Create a disk:
  2. Attach a data disk
  3. Format the data disk based on the operating system:
Encrypt the data stored on a disk Encryption overview
Resize a system disk

For more information about resizing, see Overview.

For more information, see the following topics:
  1. Resize a disk:
  2. Extend a partition and a file system:
Resize a data disk

For more information about resizing, see Overview.

For more information, see the following topics:
  1. Resize a disk:
  2. Extend a partition and a file system:
Replace a system disk Replace the system disk (public images)
Back up disk data
Copy the operating system and application data of an ECS instance Create a custom image from a snapshot
Restore a disk to its initial status Reinitialize a system disk
Restore a disk to its status at a specific point in time Roll back a disk
Release a subscription disk that is no longer needed
  1. Convert the billing method of a cloud disk
  2. Detach a data disk
  3. Release a disk
Release a pay-as-you-go disk that is no longer needed
  1. Detach a data disk
  2. Release a disk