Block Storage is a high-performance, low latency block storage service for Alibaba Cloud ECS. It supports random or sequential read and write operations. Block Storage 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 needs of your business.

Block Storage devices

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

Block Storage device Description
Disk Disks are block-level storage devices provided by Alibaba Cloud for ECS instances. 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 Cloud disk overview.
Shared Block Storage Shared Block Storage devices are block-level storage devices to which multiple ECS instances can perform concurrent reads and writes. Similar to disks, Shared Block Storage devices use a triplicate distributed mechanism. They allow multiple instances to perform concurrent access to them, and feature low latency, high performance, and high reliability. Shared Block Storage devices are ideal for the scenarios where shared access to storage resources are required in a shared-everything environment. For more information, see Shared Block Storage.
Local disk Local disks are physical disks attached to physical servers that host the ECS instances. They provide local storage access capability for ECS instances. They are designed for business scenarios that require high storage I/O performance, massive storage, and high cost-effective performance. Local disks feature low latency, high random IOPS and throughput, and excellent cost-effective performance. For more information, see Local disks.

Service performance

For 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 disks and Shared Block Storage devices 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 technology.

  • Proactive backup

    You can create snapshots at regular intervals to enhance your data security. Snapshots are backup services provided by Alibaba Cloud. They provide data backup capabilities for disks and Shared Block Storage devices, ensuring 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 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 measures are used to ensure all data is erased:
    • To make full use of the high bandwidth and low latency features of sequential write to a physical disk, the storage system appends data to an existing file at the underlayer of a disk in sequence. Based on the features of appending data to an existing file, deleting the logical space of a disk 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 disk or a Shared Block Storage device, 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 (disk) is released, the storage system destroys the metadata 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

    For data-sensitive applications, we recommend that you encrypt the storage devices that you use. 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 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 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 the three 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 as you would with a physical disk. Block Storage can meet the data storage needs 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 using APIs. OSS is applicable to the business scenarios such as website construction, separation of dynamic and static resources, and the acceleration of domain name access by using CDN. For more information, see What is OSS?.
Apsara File Storage NAS A storage space designed for storing massive unstructured data that can be accessed by using 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 suitable for 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?.