Elastic Block Storage devices - Elastic Compute Service - Alibaba Cloud Documentation Center

Elastic Block Storage (EBS) is a high-performance, low-latency block storage service provided by Alibaba Cloud for Elastic Compute Service (ECS). EBS supports random read and write to meet the data storage requirements of your business. EBS devices can be used as physical hard disks. You can partition and format EBS devices and create file systems for them.

EBS devices

Alibaba Cloud provides a variety of EBS devices for ECS, such as cloud disks based on a distributed storage architecture and local disks located on the same physical machine that hosts the associated ECS instances.


EBS device		Description	References
Cloud disk	ESSD AutoPL disk	You can specify provisioned performance and enable performance burst for ESSD AutoPL disks based on your business requirements. ESSD AutoPL disks inherit the features and performance of enhanced SSDs (ESSDs) and provide the capability of decoupling disk capacity from disk performance. We recommend that you use ESSD AutoPL disks in the following scenarios: Scenarios to which ESSDs are applicable, such as large-sized online transactional processing (OLTP) databases, NoSQL databases, and Elasticsearch, Logstash, and Kibana (ELK) distributed logs. Scenarios in which disk performance needs to be increased without extending disk capacity. Scenarios in which business workloads significantly fluctuate and disks need to burst their performance when workload spikes occur.	ESSD AutoPL disks
	ESSD	ESSDs utilize a next-generation distributed block storage architecture and provide 25 Gibabit Ethernet and remote direct memory access (RDMA). Each ESSD has low one-way latency and can deliver up to 1,000,000 random read/write IOPS. We recommend that you use ESSDs for scenarios such as OLTP databases, NoSQL databases, and ELK distributed logs.	ESSDs
	Standard SSD	Standard SSDs are high-performance disks that offer 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.	Disks
	Ultra disk	Ultra disks are cost-effective and offer 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.	Disks
	Basic disk	Basic disks are the previous generation of disks and are unavailable for purchase.	None
Local disk		Local disks are physical disks attached to physical machines that host ECS instances. Local disks provide local storage for ECS instances. They are applicable to business scenarios that require high storage I/O performance, a large amount of storage, and high cost-effectiveness. Local disks provide low latency, high random IOPS and throughput, and high cost performance. Note All of the local disks for an instance reside on a single physical machine. This increases the risks of single points of failure (SPOFs). The durability of data stored in a local disk is determined by the reliability of the associated physical machine. To ensure data availability, we recommend that you implement data redundancy at the application layer. You can use deployment sets to distribute ECS instances across multiple physical machines for high availability and disaster recovery.	Local disks

Service performance

Different EBS devices deliver different performance.

For more information about the performance of cloud disks, see EBS performance.
For more information about the performance of local disks, see Local disks.

Data security

Note The following features (except for the data erasure mechanism) are available on cloud disksbut are unavailable on local disks.

Data durability during read and write operations
Three copies of your business data are stored in a block storage cluster within the same zone to ensure 99.9999999% (nine 9's) data durability during read and write operations. For more information, see Triplicate storage.
Proactive backup
You can create snapshots for disks on a regular basis to enhance data security. Snapshots are a backup service provided by Alibaba Cloud.They back up data stored on disks to ensure that data such as logs and customer transactions can be queried. For more information, see Snapshot overview.
Data erasure mechanism
When you delete a piece of data, the data is completely erased from the distributed block storage system and can no longer be accessed by other users. The following mechanisms ensure that deleted data is completely erased:
- The storage system performs sequential writes to append data to existing files at the underlying layer of cloud disks. This mechanism makes full use of high-bandwidth and low-latency sequential writes to physical disks. If you delete a logical space from a cloud disk after data is appended at the underlying layer of the 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 that resides in the logical space of a cloud disk, the storage system does not immediately overwrite the data in the corresponding physical space. Instead, it modifies the mapping between the logical space and the physical space. This ensures that data that has been overwritten is no longer readable. Data fragments that result from delete or overwrite operations are forcefully and permanently deleted from the underlying physical disks.
- When an EBS device (cloud disk) is released, the storage system immediately destroys the metadata of the device to ensure that the data is no longer accessible. At the same time, the physical storage space that corresponds to the disk is recycled. The physical storage space must be cleared before it is re-assigned to store data. Before data is written to a new cloud disk, the system returns only zero for all read requests.
Data encryption
If your applications are data-sensitive, we recommend that you encrypt the storage devices that you use. Cloud disks and their snapshots are encrypted by using keys based on the industry-standard AES-256 algorithm. Data is automatically encrypted when it is transmitted from ECS instances to cloud disks. Encrypted data is automatically decrypted when it is read. For more information, see Encryption overview.

Billing

For information about the billing methods and billable items of EBS, see Billing overview and Block storage devices.

Limits

For information about the limits and quotas of EBS devices, see the "Elastic Block Storage (EBS) limits" in Limits.

Operations

The following figure shows common operations that can be performed on a cloud disk throughout its lifecycle. Features of cloud disks


Phase	Scenario	Description
Creation phase	Create an empty cloud disk or a cloud disk that contains backup data for an ECS instance.	Create an empty cloud disk. Create a disk Attach a data disk Initialize the data disk and create file systems for it. Initialize a data disk whose size does not exceed 2 TiB on a Linux instance Initialize a data disk up to 2 TiB in size on a Windows instance Create a cloud disk that contains backup data. Create a disk from a snapshot Attach a data disk
O&M phase	View the basic information and monitoring data of cloud disks.	Query the serial number of a disk View the monitoring data of a disk
	Use the snapshot feature to back up and restore data stored in cloud disks.	Create a snapshot of a disk Roll back a disk by using a snapshot
	Upgrade the specifications of cloud disks that do not meet your performance requirements.	Change the category of a disk Modify the performance levels of ESSDs Modify the performance configurations of an ESSD AutoPL disk
	Resize the storage capacity of cloud disks that do not meet your performance requirements.	Step 1: Resize a disk to extend its capacity Resize disks offline for Linux and Windows instances Extend the partitions and file systems of disks on a Linux instance Extend the partitions and file systems of a disk on a Windows instance
	If you want to restore cloud disks to their initial states, you can initialize the disks.	Re-initialize a system disk Re-initialize a data disk
	If you want to use a new operating system, you can change the operating system of an instance by replacing the system disk.	Replace the operating system of an instance Replace the operating system of an instance by using a non-public image
Release phase	When a cloud disk is no longer needed, you can release it to minimize costs.	Release a pay-as-you-go disk: Detach a data disk Release a disk Release a subscription disk: Change the billing method to pay-as-you-go: Change the billing methods of a disk Detach a data disk Release a disk

Local disks can be created and released only along with instances of specific instance types, and can be used as data disks and formatted. For more information, see the following topics:

Other Alibaba Cloud storage services

In addition to EBS, Object Storage Service (OSS) and Apsara File Storage NAS are storage services provided by Alibaba Cloud. For more information, see What is OSS? and What is NAS?.