Disks are block-level data storage products provided by Alibaba Cloud for ECS and feature low latency, high performance, high durability, and high 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 failures) within a zone, data within that zone is copied to an available disk in another zone to help ensure data availability.

Disk categories

Disks are classified into the following categories based on their performance:
  • Enhanced SSDs (ESSDs): 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 can deliver up to one million input/output operations per second (IOPS) and has low latency. For more information, see Enhanced SSDs.

    We recommend that you use ESSDs for scenarios such as online transactional processing (OLTP) databases, NoSQL databases, and Elasticsearch, Logstash, and Kibana (ELK) log analysis.

  • Standard SSDs: Standard SSDs are high-performance disks that feature consistent and high random IOPS and high data reliability.

    We recommend that you use standard SSDs for scenarios such as I/O-intensive applications, small and medium-sized relational databases, and NoSQL databases.

  • Ultra disks: Ultra disks are cost-effective and have medium random IOPS and high data reliability.

    We recommend that you use ultra disks for scenarios such as development and testing business and system disks.

  • Basic disks: Basic disks are the previous generation of disks and are unavailable for purchase.

For more information about disk performance, see EBS performance.

Cloud disks are classified into system disks and data disks based on their purposes.
  • System disks contain operating systems and can only be created along with instances. The lifecycle of a system disk is the same as that of the instance to which it is attached.
  • Data disks are used to store application data and can be created separately or along with instances.
Note When a disk is created, the disk capacity displayed in the ECS console includes the capacity occupied by the operating 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.

The following table describes other limits.

Item Limit How to apply for an extension on the limit
Permissions to create a pay-as-you-go disk You must complete real-name verification before you can create a disk within a region in mainland China. None.
Quota for pay-as-you-go disks in all regions for an account This quota is calculated by using the following formula: Number of ECS instances across all regions × 5. A minimum of ten pay-as-you-go disks can be created in each account. If only one instance exists in your account, you can create a maximum of ten pay-as-you-go disks in all regions, instead of five pay-as-you-go disks. Submit a ticket.
Quota for the capacity of pay-as-you-go disks that are used as data disks in an account This limit is subject to ECS resource usage, region, and disk category. You can go to the Privileges & Quotas page in the ECS console to view this information. For more information, see View and increase quotas (new version). Submit a ticket.
Quota for system disks on an instance 1 None.
Quota for data disks on an instance 16. None.
Capacity of a basic disk 5 GiB to 2,000 GiB. None.
Capacity of a standard SSD 20 GiB to 32,768 GiB. None.
Capacity of an ultra disk 20 GiB to 32,768 GiB. None.
Capacity of an enhanced SSD (ESSD) 20 GiB to 32,768 GiB. None.
Capacity of a local SSD 5 GiB to 800 GiB. None.
Total capacity of all local SSDs on an instance 1,024 GiB. None.
Capacity of a system disk
  • Windows Server: 40 GiB to 500 GiB
  • CoreOS and FreeBSD: 30 GiB to 500 GiB
  • Linux systems excluding CoreOS: 20 GiB to 500 GiB
None.
Permissions to attach new local disks to instances that are equipped with local disks Not allowed. None.
Permissions to change configurations of instances that are equipped with local disks Only bandwidth configurations of instances that are equipped with local disks can be changed. None.
Mount points of system disks /dev/vda None.
Mount points of data disks /dev/vd[b-z] None.

Billing methods

For more information, see the Pricing tab on the Elastic Compute Service page.

Disks support the subscription and pay-as-you-go billing methods. For more information, see Subscription and Pay-as-you-go.

  • Disks that are created along with subscription instances or created separately for subscription instances are billed on a subscription basis.
  • Disks that are created along 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 bills of pay-as-you-go disks.

After a disk is created, you can change its billing method. For more information, see Change billing methods of disks.

Related operations

The following table describes the operations that you can perform on disks.

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 and use a data disk
  1. Create a pay-as-you-go disk
  2. Attach a data disk
  3. Format the data disk based on the operating system:
Encrypt data stored on a disk For more information, see Encryption overview.
For more information, see the following topics:
Resize a system disk or data disk

For more information about resizing, see Overview.

For more information, see the following topics:
Replace a system disk Replace the system disk (public images)
Back up disk data
Restore a disk to its initial status Reinitialize a system disk
Restore a disk to its status at a specific point of time Roll back a disk
Detach the damaged system disk of an instance and attach the disk back to the original instance after the disk is repaired Detach or attach a system disk
Release an instance and retain data stored on its system disk
Release a subscription disk that is no longer needed
  1. Change billing methods of disks
  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