Cloud disks are block-level Elastic Block Storage (EBS) products provided by Alibaba Cloud for ECS and provide low latency, high performance, high durability, and high reliability. Cloud disks use a distributed triplicate mechanism to ensure 99.9999999% (nine 9's) data durability for ECS instances. If service disruptions occur within a zone (for example, due to hardware failures), data within the zone is copied to an available disk in another zone to help ensure data availability.

Disk categories

Cloud 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 has low latency and can deliver up to one million input/output operations per second (IOPS). For more information, see ESSDs.

    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 provide consistent 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 provide medium random IOPS and high data reliability.

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

  • 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 purpose.
  • System disks contain operating systems and can be created only along with instances. The lifecycle of a system disk is the same as that of the instance to which the system disk is attached.
  • Data disks are used to store application data and can be created separately or along with instances.
Note When a cloud 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 cloud disk can be attached to only one ECS instance in the same zone.

The following table describes other limits.

Item Limit Adjustable
Permissions to create pay-as-you-go disks To create disks within in mainland China regions, you must first complete real-name verification. N/A
Pay-as-you-go disks You can view the resource quota in the ECS console. For more information, see View and increase resource quotas. N/A
System disks on an instance 1 N/A
Data disks on an instance You can attach up to 64 data disks to a g6se instance and up to 16 data disks to an instance of other instance families. N/A
Total capacity of all pay-as-you-go ultra disks within an account You can view the resource quota in the ECS console. For more information, see View and increase resource quotas. N/A
Total capacity of all pay-as-you-go standard SSDs within an account You can view the resource quota in the ECS console. For more information, see View and increase resource quotas. N/A
Total capacity of all pay-as-you-go enhanced SSDs (ESSDs) within an account You can view the resource quota in the ECS console. For more information, see View and increase resource quotas. N/A
Capacity of a single basic disk 5 GiB to 2,000 GiB N/A
Capacity of a single standard SSD 20 GiB to 32,768 GiB N/A
Capacity of a single ultra disk 20 GiB to 32,768 GiB N/A
Capacity of a single ESSD 20 GiB to 32,768 GiB N/A
Capacity of a single local SSD 5 GiB to 800 GiB N/A
Total capacity of all local SSDs on an instance 1,024 GiB N/A
Capacity of a single system disk
  • Windows Server: 40 GiB to 500 GiB
  • Red Hat: 40 GiB to 500 GiB
  • CoreOS and FreeBSD: 30 GiB to 500 GiB
  • Linux systems excluding CoreOS: 20 GiB to 500 GiB
N/A
Permissions to attach new local disks to instances that are equipped with local disks You cannot attach new local disks to instances that are already equipped with local disks. N/A
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. N/A
Mount points of system disks /dev/vda N/A
Mount points of data disks /dev/vd[b-z] N/A

Billing methods

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

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

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

After a cloud 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 cloud 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 disk
  2. Attach a data disk
  3. Format the data disk based on the operating system:
Encrypt data stored on a cloud disk Encryption overview
Resize a system disk or a data disk

Overview

Replace a system disk Replace the system disk (public images)
Back up disk data
Restore a disk to its initial status Re-initialize a system disk
Restore a disk to its status at a specific point in time Roll back a disk by using a snapshot
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