Elastic block storage is a low-latency, high-performance, persistent, and high-reliability block-level data storage service provided by Alibaba Cloud to ECS users. It uses a triplicate distributed system to provide 99.9999999% data reliability for ECS instances. Elastic block storage supports the automatic copying of your data within the zone. It prevents unexpected hardware faults from causing data unavailability and protects your service against the threat of component faults. As with a hard disk, you can partition and format the elastic block storage attached to an ECS instance, create a file system, and store data on it.

You can expand your elastic block storage as needed at any time. For more information, see Linux _ Resize a data disk or Increase system disk size. You can also create snapshots to back up data for the elastic block storage.  For more information about snapshots, see What are ECS snapshots.

Based on whether it can be attached to multiple ECS instances, the elastic block storage can be divided into:

  • Cloud disks: Can be attached to only one ECS instance in the same zone of the same region.
  • Shared Block Storage: Can be attached to up to eight ECS instances in the same zone of the same region.
    Note
    The Shared Block Storage is currently in public beta. You can open a ticket to apply for beta qualification.

Cloud disks

Based on performance,

cloud disks can be divided into:

  • SSD Cloud Disk: High-performance disks with stable and high random I/O performance and high data reliability.
  • Ultra Cloud Disk: With high cost performance, medium random I/O performance, and high data reliability.
  • Basic Cloud Disk: With high data reliability and general random I/O performance.
Cloud disks can be used

as:

  • System disks: Has the same lifecycle as the ECS instance it is attached to. It is created and released along with the instance. Shared access is not allowed. The available size range of a single system disk varies according to the image:
    • Linux (excluding CoreOS) and FreeBSD: 20−500 GiB
    • CoreOS: 30−500 GiB
    • Windows: 40−500 GiB
  • Data disks: Can be created separately or jointly with ECS instances. Shared access is not allowed. The data disk created with an ECS instance has the same lifecycle as the instance, and is created and released along with the instance. Separately created data disks can be released independently or with ECS instances. The performance of data disks depends on the cloud disk type. For more information, see Storage parameters and performance test.

When used as data disks, up to 16 cloud disks can be attached to one ECS instance.

Shared Block Storage

Shared Block Storage is a block-level data storage service with high level of concurrency, performance, and reliability. It supports concurrent reads and writes to multiple ECS instances, and provides data reliability of up to 99.9999999%. Shared Block Storage can be attached to a maximum of eight ECS instances.

Shared Block Storage can only be used as data disks and can only be created separately. Shared access is allowed. You can set the Shared Block Storage to be released when the ECS instances are released.

Based on different performance, the Shared Block Storage can be divided into:

  • SSD Shared Block Storage: Adopts SSD as the storage medium to provide stable and high-performance storage with enhanced random I/O and data reliability.
  • Ultra Shared Block Storage: Adopts the hybrid media of SSD and HDD as the storage media.

When used as data disks, Shared Block Storage allows up to 16 data disks to be attached to each ECS instance.

For more information, see FAQ about Shared Block Storage.

Billing

Shared Block Storage is currently in public beta, during which it is free of charge.

The billing method of a cloud disk depends on how it is created:

  • Cloud disks created with Subscription (monthly or yearly subscription) instances are billed by upfront payment before the service is ready for use. For more information, see Subscription.
  • Cloud disks created jointly with Pay-As-You-Go instances, or created separately, are billed on a Pay-As-You-Go basis. For more information, see Pay-As-You-Go.

Information about changing the billing method of a cloud disk is shown in the following table.

Conversion of billing methods Features Effective date Suitable for
Subscription —> Pay-As-You-Go Renew for configuration downgrade Effective from the next billing cycle Subscription cloud disks attached to Subscription instances. The billing method of the system disk cannot be changed.
Pay-As-You-Go —> Subscription Upgrade configurations. Effective immediately Pay-As-You-Go data disks attached 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 attached to Pay-As-You-Go instances.

Related operations

You can perform the following operations on an elastic block storage:

For more information about the operations on cloud disks, see the Cloud disks section in the User Guide.