Block Storage is a high-performance, low-latency block storage service that is provided by Alibaba Cloud for Elastic Compute Service (ECS). Block Storage supports random reads and writes to meet your data storage requirements in most common business scenarios. Block Storage includes Elastic Block Storage (EBS) and local storage. You can use block storage devices in the same manner that you use physical hard disks. You can format block storage devices on ECS instances and create file systems for the devices. This topic describes the categories of block storage devices and common operations that you can perform on block storage devices.
Categories of block storage devices
Alibaba Cloud provides various block storage devices for ECS, including cloud disks that are based on a distributed storage architecture, local disks that are attached to physical machines, and elastic ephemeral disks.
Cloud disks
Cloud disks are block-level data storage devices provided by Alibaba Cloud for ECS. Cloud disks use a distributed triplicate mechanism to achieve 99.9999999% (nine 9's) data durability for ECS instances.
Cloud disk categories by usage
Cloud disk category
Description
System disks
System disks are the boot disks of ECS instances and are used to store system-related data, such as operating systems and program files. System disks can be created only together with ECS instances and have the same lifecycle as the instances.
Data disks
Data disks are used to store non-system-related data, such as user data, logs, and applications. Data disks can be created separately or together with ECS instances.
Cloud disk categories by performance
Cloud disks are classified based on disk performance into Enterprise SSD (ESSD)-series disks and disks of the previous generation, which include standard SSDs, ultra disks, and basic disks. The following table provides a comparison of the different cloud disk categories.
ESSD-series disks
Cloud disk category
Feature
Usage scenario
Billing
Decouple disk capacity from disk performance.
Support the performance provision feature.
Support the performance burst feature.
All scenarios for which ESSDs are suitable.
Scenarios in which disk performance needs to be increased without the need for disk capacity extension.
Scenarios in which business workloads significantly fluctuate and disks need to burst their performance when workload spikes occur.
You are charged for disk capacity.
You are charged for the provisioned performance on a pay-as-you-go basis after the performance provision feature is enabled.
You are charged for the burst performance on a pay-as-you-go basis after the performance burst feature is enabled.
Deliver high IOPS.
Provide zone-redundant storage.
All scenarios for which ESSDs are suitable.
Multi-zone disaster recovery for databases.
Cross-zone container deployment.
Self-managed or cloud-based Software as a Service (SaaS) services.
You are charged for disk capacity.
Deliver high IOPS.
Deliver low latency.
Latency-sensitive applications or I/O-intensive business scenarios, such as:
Large-scale online transaction processing (OLTP) databases
NoSQL databases
Elasticsearch distributed logs
You are charged for disk capacity.
ESSD Entry disks
NoteESSD Entry disks can be attached to only instances of universal instance families and e economy instance families.
Deliver high IOPS.
Deliver low latency.
Development and testing business
Usage as system disks.
You are charged for disk capacity.
Cloud disks of the previous generation
Standard SSDs, ultra disks, and basic disks are cloud disks of the previous generation and are unavailable for purchase in specific regions and zones. We recommend that you use ESSDs at performance level 0 (PL0 ESSDs) or ESSD Entry disks instead of ultra disks and basic disks and use ESSD AutoPL disks instead of standard SSDs.
Cloud disk category
Feature
Usage scenario
Billing
Standard SSDs
Deliver high random read/write performance.
Provide high reliability.
I/O-intensive applications
Small and medium-sized relational databases and NoSQL databases
You are charged for disk capacity.
Ultra disks
Deliver high cost efficiency.
Provide high reliability.
Development and testing business
Usage as system disks.
You are charged for disk capacity.
Basic disks
Deliver high cost efficiency.
Low-cost development and testing business that does not require high storage performance
You are charged for disk capacity.
Local disks
Local disks provide local storage for ECS instances and reside on the physical machines that host the instances. Local disks are suitable for scenarios that require high storage I/O performance, mass storage, and high cost efficiency. Alibaba Cloud provides two categories of local disks. The following table describes the categories.
Category | Supported instance family | Scenario |
Local non-volatile memory express (NVMe) SSD | The following instance families use local NVMe SSDs:
| Instance families equipped with local NVMe SSDs are suitable for the following scenarios:
|
Local SATA HDD | The d3s, d2c, d2s, d1ne, and d1 big data instance families use local SATA HDDs. | Local SATA HDDs are the preferred storage media for industries such as Internet and finance that have high requirements for big data computing, storage, and analytics. These disks are suited for mass storage and offline computing scenarios and can meet the high requirements of distributed computing services such as Hadoop in terms of storage performance, storage capacity, and internal network bandwidth. |
This topic describes the local disks that are purchased together with ECS instances. For information about the performance of instance families that are equipped with local SSDs and big data instance families, see Overview of instance families.
For more information about local disks, see Local disks.
Elastic ephemeral disks
An elastic ephemeral disk is a block storage device that can be created alongside an ECS instance or separately created, with user-defined capacity for temporary data storage. It features high performance and cost-effectiveness. For more information, see Elastic ephemeral disks.
Performance of block storage devices
The performance of block storage devices varies based on the device category.
For information about the performance of cloud disks, see the Performance of cloud disks section in the "Block storage performance" topic.
For information about the performance of local disks, see the Performance of local disks section in the "Block storage performance" topic.
For information about the performance of elastic ephemeral disks, see the Performance of elastic ephemeral disks section in the "Block storage performance" topic.
Data security
The following features, except for the data erasure mechanisms, are unique to cloud disks and elastic ephemeral 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. Snapshot is a backup service provided by Alibaba Cloud. Snapshots back up the data that is stored on disks and ensure that data, such as logs and customer transaction data, can be queried. For more information, see Overview of snapshots.
Data erasure mechanisms
When you delete data, the data is completely erased from the distributed block storage system and can no longer be accessed by other users. The following mechanisms are used to 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 fully utilizes 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, the delete operation is recorded as metadata. The storage system returns only zeros for all requests of reading data from the logical space. Similarly, when you overwrite data that is stored in the logical space of a cloud disk, the storage system does not immediately overwrite the data in the corresponding physical space. Instead, the storage system modifies the mapping between the logical space and the physical space to ensure that the overwritten data is no longer readable. Data fragments caused by delete or overwrite operations are forcefully and permanently deleted from the underlying physical disks.
When you release an EBS device (cloud disk), the storage system immediately destroys the metadata of the device to ensure that the disk data is no longer accessible. At the same time, the physical storage space of the device is recycled. The physical storage space must be cleared before the storage space is re-assigned. Before data is written to a new cloud disk, the system returns only zeros 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 the snapshots of the disks are encrypted by using keys based on the industry-standard AES-256 algorithm. Data is automatically encrypted when the data is transferred from ECS instances to cloud disks. Encrypted data is automatically decrypted when the data is read. For more information, see Encrypt cloud disks.
Billing
For information about the billing methods and billable items of Block Storage, see Block storage devices.
Limits
For information about the limits and quotas of Block Storage, see the Block storage limits section in the "Limits" topic.
Operations
Common operations on cloud disks
You can create a cloud disk together with an ECS instance or separately create a cloud disk. For information about the common operations that you can perform on a cloud disk, see Quickly create and use a cloud disk.
Common operations on local disks
You can create and release local disks only together with instances of specific instance types. For more information, see Local disks.
Common operations on elastic ephemeral disks
Elastic ephemeral disks can be created alongside an ECS instance or separately created. For more information, see Use elastic ephemeral disks.
Other Alibaba Cloud storage services
In addition to Block Storage, Alibaba Cloud provides other storage services, such as Object Storage Service (OSS) and File Storage NAS (NAS), to meet your business requirements in different scenarios. For more information, see Comparison of NAS, OSS, and EBS.