The Alibaba Cloud snapshot service is an agentless backup service that allows you to create crash-consistent snapshots for all disk categories. Crash-consistent snapshots are an effective solution to disaster recovery and can be used to back up data, restore disks, create custom images, and implement disaster recovery for applications.

Introduction

A snapshot is a point-in-time backup of a disk. The first snapshot of a disk is a full snapshot that does not contain the copies of empty data blocks. Subsequent snapshots are incremental snapshots that store only changed data blocks. For more information, see Incremental snapshots.

The following figure shows common snapshot features.Scenarios
Feature Description Reference
Create a snapshot You can use the following methods to create snapshots:
  • You can manually create snapshots. Manually created snapshots are called manual snapshots. You can create manual snapshots before you perform high-risk operations to improve fault tolerance.
  • You can create automatic snapshot policies to create snapshots. Snapshots created based on these policies are called automatic snapshots. After you create an automatic snapshot policy and apply it to a disk, the system automatically creates snapshots for the disk at the points in time specified in the policy. You can use automatic snapshots to back up data and improve the security of your business data.
Roll back a disk When the system is unresponsive or when an incorrect operation is performed, you can roll back a disk to a previous version by using one of its snapshots. Roll back a disk by using a snapshot
Create an image from a system disk snapshot You can create a custom image from a snapshot that contains the operating system and data of an ECS instance. Then, you can use the custom image to create multiple instances that have identical application environments. Create a custom image from a snapshot
Create a disk from a snapshot A single snapshot can be used to create multiple identical disks. Create a disk from a snapshot
Copy a snapshot from other regions When a snapshot is copied from one region to another, a copy of the snapshot is created in the destination region. Copy a snapshot

In addition, the snapshot service provides advanced features such as instant access. For more information, see Enable or disable the instant access feature.

Billing

Snapshots are billed based on their size and use the pay-as-you-go billing method. For more information, see Snapshots.

Note Pay-as-you-go bills of snapshots can be offset by storage capacity units (SCUs).

Limits

For the limits and quotas of snapshots, see the "Snapshot limits" section in Limits.

Scenarios

You can use snapshots for the following scenarios:
  • Disaster recovery and backup: You can create a snapshot for a disk and then use the snapshot to create another disk to implement zone- or geo-disaster recovery.
  • Environment clone: You can use a system disk snapshot to create a custom image and then use the custom image to create ECS instances that have identical environments.
  • Improvement of fault tolerance: You can reduce the risk of data loss caused by incorrect operations by using a snapshot to roll a disk back to a previous version. Snapshots are suitable for the following scenarios:
    • Create snapshots on a regular basis to prevent data loss caused by incorrect operations or external attacks. Incorrect operations include: writing invalid data to disks, accidentally releasing ECS instances, data errors caused by application errors, and data loss due to hacking.
    • Create snapshots before you perform high-risk O&M operations, such as replacing operating systems, upgrading applications, and migrating data.

Benefits

The following table describes the benefits of Alibaba Cloud ECS snapshots compared with snapshots in traditional storage services.
Item Alibaba Cloud ECS snapshot Traditional storage service snapshot
Capacity Unlimited capacity for storing large amounts of business data. Limited capacity, dependent on the capacity of the storage device.
Scalability High scalability allows you to extend storage devices to any sizes within seconds. Low scalability, dependent on the storage performance, available capacity, and vendor support.
Total cost of ownership (TCO) You need only to pay for the amount of storage space occupied by your snapshots. High upfront costs for software licenses, reserved storage space, upgrade, and maintenance.
Security Supports data encryption. After you encrypt a disk, all snapshots that are created for it are also encrypted. Unencrypted snapshots cannot be directly converted to encrypted snapshots, and encrypted snapshots cannot be directly converted to unencrypted snapshots. For more information, see Encryption overview. Encryption attributes and policies are subject to the underlying storage logic. If the storage architecture has security flaws, snapshots created based on this architecture may not be secure.
Impact on performance Uses redirect-on-write (ROW).
  • Impacts on the I/O performance of the source disk are reduced.
  • Snapshots do not affect service availability and can be created at any time without affecting user experience.
Typically uses copy-on-write (COW), but may also use ROW or other methods. COW may affect the data write capabilities of the source system.