Block Storage is a high-performance, low-latency block storage service for Alibaba Cloud ECS. It supports random read and write operations. A Block Storage device is similar to a physical disk. You can format a Block Storage device and create a file system on it to meet the data storage requirements of your business.

Block Storage devices

Alibaba Cloud provides a variety of Block Storage devices for ECS instances, such as cloud disks based on a distributed storage architecture, and local disks located on the physical machines where the ECS instances are hosted.

Block Storage device Description
Cloud disk Cloud disks are block-level storage devices provided by Alibaba Cloud for ECS instances. Cloud disks use a triplicate distributed mechanism and feature low latency, high performance, durability, and high reliability. Disks can be created, resized, and released at any time. For more information, see Disk overview.
Local disk Local disks are physical disks attached to physical machines that host ECS instances. Local disks provide local storage access capabilities for ECS instances. They are designed for business scenarios that require high storage I/O performance, a large amount of storage, and high cost-effective performance. Local disks feature low latency, high random IOPS and throughput, and excellent cost-effective performance.
Note Local disks are attached to a single physical machine, which increases the risk of single point of failure (SPOF) because the reliability of data is dependent on the reliability of the physical machine. We recommend that you implement data redundancy at the application layer to ensure data availability and enhance business continuity. You can use deployment sets to distribute ECS instances across multiple physical machines to implement high availability and disaster recovery. For more information, see Local disks.

Service performance

For more information about the performance of each type of Block Storage devices, see Block Storage performance.

Data security

Note Except for the data erasure mechanism, only cloud disks have the following features.
  • Data reliability during read and write operations

    Three copies of your business data are stored in the Block Storage cluster in the same zone to ensure 99.9999999% data reliability during read and write operations. For more information, see Triplicate storage.

  • Proactive backup

    You can create snapshots at regular intervals to enhance your data security. Snapshots are a backup service provided by Alibaba Cloud. They provide data backup capabilities for cloud disks to ensure that information such as logs and customer transactions are backed up. For more information, see Snapshot overview.

  • Data erasure mechanism
    When you delete a piece of data from cloud disks and Share Block Storage devices, it is completely erased from the distributed Block Storage system and can no longer be accessed by other users in any way. The following mechanisms are used to ensure that all data is erased:
    • The storage system performs sequential writes to append data to an existing file at the underlying layer of a cloud disk. This mechanism makes full use of the high-bandwidth and low-latency features of sequential write to a physical disk. Based on the features of appending data to an existing file, if you delete the logical space of a cloud disk, this operation is recorded as metadata. The storage system returns only zero for all requests of reading data from the logical space. Similarly, when you overwrite the data in the logical space of a cloud disk, the storage system does not directly overwrite the data in the logical space, but modifies the mapping between the logical space and the physical space. This ensures that data that has been overwritten can no longer be read. Data fragments that result from delete or overwrite operations are forcibly and permanently deleted from the underlying physical disks.

    • When a Block Storage device (cloud disk) is released, the storage system destroys the metadata of the device immediately to ensure that the data can no longer be accessed. At the same time, the physical storage space corresponding to the disk is recycled. The physical space must be cleared before it is re-assigned to store data. Before data is written to a new disk, the system returns only zero for all read requests.

  • Data encryption

    We recommend that you encrypt the storage devices that you use if your applications are data-sensitive. Cloud disks and their snapshots are encrypted with keys based on the industry-standard AES-256 algorithm. Data is automatically encrypted when it is transmitted from ECS instances to cloud disks and automatically decrypted when the data is read. For more information, see Encryption overview.


For more information about the billing methods and pricing of Block Storage devices, see Billing overview.


For more information about the limits and quotas of Block Storage devices, see the "Block Storage limits" section in Limits.

Differences among Alibaba Cloud storage services

Alibaba Cloud provides the following three data storage services: Block Storage, Object Storage Service (OSS), and Apsara File Storage NAS. The following table lists the differences among these data storage services.
Data storage service Description
Block Storage A high-performance and low-latency block-level storage device provided by Alibaba Cloud for ECS instances. It supports random read and write operations, and can be attached to ECS instances as a system disk or data disk. You can partition and format a Block Storage device and create file systems on it in the same way as you do with a physical disk. Block Storage can meet the data storage requirements of most business scenarios.
OSS A huge storage space designed to store unstructured data on the Internet, such as images, audios, and videos. You can access the data stored in OSS anytime and anywhere by calling API operations. OSS is applicable to the business scenarios such as website construction, separation of dynamic and static resources, and acceleration of domain name access through CDN. For more information, see What is OSS?.
Apsara File Storage NAS A storage space designed for storing a large amount of unstructured data that can be accessed based on standard file access protocols, such as the Network File System (NFS) protocol for Linux, and the Server Message Block (SMB, also called Common Internet File System (CIFS)) protocol for Windows. You can set permissions to allow different clients to access the same file at the same time. Apsara File Storage NAS is applicable to the business scenarios such as file sharing across departments in an enterprise, non-linear editing in radio and television industries, high-performance computing, and containerization. For more information, see What is Apsara File Storage NAS?.