Block Storage offers high-performance, low-latency storage. It includes cloud disks, local disks, and elastic ephemeral disks that function as physical hard drives.
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 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% (12 nines) 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 ESSDs
Use cases:
Multi-zone disaster recovery for databases, big data, middleware, Enterprise Resource Planning (ERP)/Customer Relationship Management (CRM).
Container deployments across zones.
ImportantZRS writes data to multiple zones. Write latency may be higher than LRS. See Block storage performance for details.
If the entire region fails, data becomes inaccessible. For cross-region availability, Create an automatic snapshot policy that regularly creates snapshots and copies 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% (9 nines) data reliability for ECS instances. LRS ensures data durability and availability in the event of hardware failure.
Disk types: ESSD AutoPL disk, ESSD ，ESSD PL-X disk, and ESSD Entry disk.
Use cases:
Online Transaction Processing (OLTP) databases (MySQL, PostgreSQL, Oracle), NoSQL databases (MongoDB, HBase, Cassandra) and Elasticsearch distributed logging.
System disk or replacement for Ultra/Basic disk.
Fixed capacity with variable performance needs.
Workloads with frequent traffic spikes (bursting support).
Replacement for Standard SSD.
ESSD PL-X disks (Invitational Preview): OLTP databases requiring extreme Input/Output Operations Per Second (IOPS), throughput, and latency.
ESSD Entry:
Development and testing.
System disk or replacement for Ultra/Basic disk.
ESSD Entry disks can be attached only to universal instance families (U instances) and the e, economy instance family.
Data is stored in one zone. If the zone fails, data becomes inaccessible. For higher availability, use Regional ESSDs.
Example: Regional ESSDs vs ESSD PL1
Feature | Regional ESSDs | ESSD PL1 |
Redundancy | Zone-redundant storage (ZRS) | Locally redundant storage (LRS) |
Durability | 99.9999999999% (12 nines) | 99.9999999% (9 nines) |
Max IOPS (Input/Output Operations Per Second) | 50,000 | 50,000 |
Max throughput (MB/s) | 350 | 350 |
Avg write latency (4K blocks) | Millisecond-level | 0.2 ms |
Attachment scope | Attach to instances in any zone within the region. | Attach only to instances in the same zone as the disk. |
Single-zone failure impact | No service disruption | Service unavailable |
Price (Hangzhou, monthly) | ¥1.5/GB/month | ¥1/GB/month |
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
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
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)
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
Ultra-high IOPS
Ultra-high throughput
Ultra-low latency
Supports provisioned performance
OLTP and KV databases that require higher disk IOPS, throughput, and lower latency
99.9999999%
Capacity fee
Provisioned performance fee (enabled by default and charged after being enabled)
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
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:
|
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. |
For more information about the performance of local SSD-equipped and big data instance families, see Instance families.
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
Except for the data erasure mechanism, the following content applies only to cloud disks and does not apply to local disks or elastic ephemeral disks.
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?.