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Elastic Compute Service:Overview of Block Storage

Last Updated:Nov 06, 2024

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 and local disks that are attached to physical machines.

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

      ESSD AutoPL disks

      • 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.

      Regional ESSDs (public preview)

      • 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.

      ESSDs

      • 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

      Note

      ESSD 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 SSDs: i4, i4g, i4r, i3, i3g, i2, i2g, i2ne, i2gne, and i1

  • GPU-accelerated compute-optimized instance family: gn5

Instance families equipped with local NVMe SSDs are suitable for the following scenarios:

  • I/O-intensive applications that require high I/O performance and low latency, such as online gaming, e-commerce, live streaming, and media

  • Applications that require high storage I/O performance and a high-availability architecture at the application layer, such as NoSQL databases (including Cassandra, MongoDB, and HBase), Massively Parallel Processing (MPP) data warehouses, and distributed file systems

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.

Note
  • 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.

Data security

Note

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 Overview.

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

The following figure shows the common operations that you can perform on a cloud disk during the cloud disk lifecycle.

image

Phase

Scenario

Operation

Creation phase

Create an empty cloud disk or a cloud disk that contains data from a snapshot for an ECS instance.

O&M phase

View the basic information and monitoring data of a cloud disk.

Use snapshots to back up and restore data of a cloud disk.

Upgrade the specifications of a cloud disk to meet your business requirements.

Extend the storage capacity of a cloud disk to meet your capacity requirements.

  1. Step 1: Resize a cloud disk to extend its capacity.

  2. Step 2: Extend partitions and file systems.

Encrypt a cloud disk to encrypt data that is stored on the disk.

Encrypt a cloud disk

If you want to restore a cloud disk to its initial state, you can re-initialize the disk.

If the system disk of an ECS instance is damaged, you can detach the disk, repair the disk, and then re-attach the disk to the instance.

Detach or attach a system disk.

If you want to use a different operating system, you can change the operating system of an instance by replacing the system disk.

Replace the operating system (system disk) of an instance.

Release phase

If you no longer require a cloud disk, you can release the disk to reduce costs.

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.