Elastic Compute Service:Overview of Block Storage

Cloud disks

Cloud disks are based on a distributed storage architecture and provide high data reliability for ECS instances.

• By purpose

  Disk type	Description
  System disk	The boot disk for an ECS instance. It stores system-related data, such as the operating system and program files. It can only be created with an ECS instance and shares the same lifecycle as the instance it is attached to.
  Data disk	Stores non-system data, such as user data, logs, and other applications. It can be created with an ECS instance or created separately.

• By performance

  Cloud disks are classified into ESSD-series disks and previous-generation disks (standard SSDs, ultra disks, and basic disks) based on performance. The following table compares the disk types.

  Because disk performance varies by disk type, select a disk that meets your workload and application requirements.

  For information about the pricing and billing of different disk types, see Billing of cloud disks.

  • ESSD-series disks

    Disk type	Features	Scenarios	Data reliability guarantee	Billing
    ESSDs	High IOPS Low latency	Latency-sensitive applications or I/O-intensive business scenarios: Large-scale online transactional processing (OLTP) databases NoSQL databases Elasticsearch distributed logs	99.9999999%	Capacity fee
    ESSD AutoPL disks	Decouples capacity from performance. Supports provisioned performance. You can flexibly configure provisioned performance as needed without changing the storage capacity. Supports performance burst. For services with fluctuating workloads, ESSD AutoPL disks temporarily increase disk performance based on actual business conditions to handle sudden data read and write pressure.	Scenarios where ESSDs are suitable Fixed disk capacity with high performance requirements Large business fluctuations with frequent peaks that require handling sudden business surges	99.9999999%	Capacity fee Pay-as-you-go provisioned performance fee (charged after being enabled) Pay-as-you-go burst performance fee (charged after being enabled)
    Regional ESSDs	High input/output operations per second (IOPS) Zone-redundant storage	Scenarios where ESSDs are suitable Multi-zone disaster recovery for databases Cross-zone container deployment Self-built or cloud-deployed Software as a Service (SaaS) services	99.9999999999%	Capacity fee
    ESSD Entry disk ESSD Entry disks can be attached only to universal instance families (U instances) and the e, economy instance family.	High IOPS Low latency	Development and testing System disk	99.9999999%	Capacity fee

  • Previous-generation disks

    Standard SSDs, ultra disks, and basic disks are previous-generation cloud disk products that are being phased out in some regions and zones. We recommend that you use PL0 ESSDs or ESSD Entry disks to replace ultra disks and basic disks, and use ESSD AutoPL disks to replace standard SSDs.

    Disk type	Features	Scenarios	Billing
    Standard SSD	High random read and write performance High reliability	I/O-intensive applications Small and medium-sized relational databases and NoSQL databases	Capacity fee
    Ultra Disk	High cost-effectiveness High reliability	Development and testing workloads Use as a system disk	Capacity fee
    Basic disk	High cost-effectiveness	Low-cost development and testing workloads that do not require high storage performance	Capacity fee

• By storage redundancy

  Cloud disks provide two storage redundancy types: zone-redundant storage and locally redundant storage. These types use data redundancy mechanisms that range from a single zone to multiple zones to ensure data durability and availability.

  • Zone-redundant storage (ZRS)

    ZRS uses a multi-zone data redundancy mechanism to store redundant copies of your data across multiple zones in the same region. In these zones, IDCs, racks, and power supplies are physically isolated. This provides 99.9999999999% data reliability for ECS instances. If a physical failure occurs in a zone, ZRS provides continuous read and write services to ensure business continuity.

    Disk type: Regional ESSD.

    Important

    Data is redundantly stored within a specific region. If the region becomes unavailable, the related data becomes inaccessible. If your business requires extremely high availability, regularly create snapshots and copy them to other regions.

  • Locally redundant storage (LRS)

    LRS uses a single-zone data redundancy mechanism to store redundant copies of your data on multiple devices in different facilities within the same zone. This provides 99.9999999% data reliability for ECS instances. LRS ensures data durability and availability in the event of hardware failure.

    Disk types include ESSD AutoPL disks, ESSDs, ESSD PL-X disks, and ESSD Entry disks.

    Important

    Data is redundantly stored within a specific zone. If the zone becomes unavailable, the related data becomes inaccessible. If your business requires higher availability, use regional ESSDs.

Local disks

Local disks are local hard disk devices on the physical machines that host ECS instances. They provide local storage access for ECS instances and are suitable for scenarios that require high storage I/O performance, mass storage, and cost-effectiveness. Alibaba Cloud provides the following two types of local disks:

Elastic ephemeral disks

An elastic ephemeral disk is a block storage device that can be created with an instance or created separately. You can customize its capacity. It provides temporary data storage space for ECS instances and features high performance and cost-effectiveness.

Data security of block storage

• Read and write stability

  Your data is stored in triplicate across a block storage cluster in the same zone. This ensures data stability during read and write operations and provides 99.9999999% data reliability for ECS instances. For more information, see Triplicate technology for cloud disks.

• Proactive backup

  You can periodically create snapshots to improve data security. Snapshots are an Alibaba Cloud backup product that provides data backup capabilities for cloud disks. This lets you back up and query information such as logs and customer transactions.

• Data erasure mechanism

  Data that you delete is inaccessible to other users. When you delete data from the distributed block storage system, it is completely erased. Data erasure integrity is ensured by the following mechanisms:

  • Cloud disks use sequential append-writes at the underlying layer. This design leverages the high bandwidth and low latency of sequential writes on physical disks. Because of the append-write feature, an operation to delete a logical space on a cloud disk is recorded only as metadata. If you attempt to read from this logical space, the storage system returns all zeros. Similarly, overwriting a logical space does not immediately overwrite the corresponding space on the physical disk. Instead, the storage system modifies the mapping between the logical and physical spaces to perform the overwrite. This ensures that the original data cannot be read. Residual data on the physical disk from delete or overwrite operations is later permanently deleted.

  • When you release a block device, such as a cloud disk, the storage system immediately destroys its metadata to make the data inaccessible. The physical storage space that the cloud disk occupied is also reclaimed. This physical space is cleared before it is reallocated. All newly created cloud disks return zeros for all read operations before the first write.

• Data encryption

  For applications with sensitive data, you can encrypt your storage devices. ECS disk encryption uses the industry-standard AES-256 algorithm to encrypt cloud disks and their snapshots with keys. Data is automatically encrypted when transferred from an ECS instance to a cloud disk and automatically decrypted when read from the disk.

References

• For information about the limits and quotas of block storage, see Limits of block storage.

• For information about common operations on cloud disks, see Guide to creating and using disks.

• In addition to ECS block storage, Alibaba Cloud also provides other storage products, such as Object Storage Service (OSS) and File Storage NAS, for different business scenarios. For more information, see How do I select a storage service from NAS, OSS, and EBS?.