Overview - Elastic Compute Service - Alibaba Cloud Documentation Center

Elastic Compute Service (ECS) uses automatic snapshot policies to create snapshots on a regular basis at scheduled points in time to protect data stored on system and data disks. You can use automatic snapshot policies to improve data security and fault tolerance.

Use scenario

Use automatic snapshots to back up data on disks that run critical applications on a regular basis. This allows you to quickly retrieve disk data to ensure business continuity if data loss or application errors occur due to reasons such as accidental operations and ransom viruses.

Usage notes

When you use automatic snapshot policies, take note of the following items:

Item	Description
Automatic snapshot policy	For information about the quota of automatic snapshot policies per region for an Alibaba Cloud account and the maximum number of automatic snapshots that can be retained for a disk, see the "Snapshot limits" section in Limits. Note If the maximum number of automatic snapshots is reached, the oldest automatic snapshot is automatically deleted when a new automatic snapshot is created. If you modify the retention period of automatic snapshots in an automatic snapshot policy, the modification is applied to subsequent snapshots but not to existing snapshots.
Disk type	Local disks do not support automatic snapshot policies. You can configure automatic snapshot policies for other types of disks.
Disk status	You can create automatic snapshots only for disks that are in the In Use state. Note If a disk is in the Unattached state and has never been attached to instances, the data that is stored on the disk remains unchanged. In this case, you do not need to create snapshots for the disk and cannot configure an automatic snapshot policy for the disk.
Create an automatic snapshot	If a snapshot is being manually or automatically created for a disk at a point in time that is designated in the associated automatic snapshot policy, the system cannot create an automatic snapshot based on the policy. An automatic snapshot is created for the disk at the subsequent point in time that is designated in the automatic snapshot policy. If an automatic snapshot is being created for a disk, you cannot create a manual snapshot for the disk. Wait until the automatic snapshot is created. Automatic snapshots are created within one hour after the points in time specified by Execution Time.
The number of automatic snapshot policies that can be configured for a single disk	1.

Common operations

The following figure shows the common operations that you can perform for automatic snapshots from the time when an automatic snapshot policy is created until the time when the automatic snapshots are released. 自动快照

Operation	Description	References
Create an automatic snapshot policy	Create an automatic snapshot policy and specify when to create automatic snapshots and how long to retain the snapshots.	Create an automatic snapshot policy CreateAutoSnapshotPolicy
Apply an automatic snapshot policy	Apply an automatic snapshot policy to a disk to automatically create snapshots for the disk on a regular basis.	Enable or disable an automatic snapshot policy ApplyAutoSnapshotPolicy
Modify an automatic snapshot policy	Modify the information of an automatic snapshot policy, such as the start time and retention period of automatic snapshots.	Modify an automatic snapshot policy ModifyAutoSnapshotPolicyEx
Create automatic snapshots on a regular basis	ECS creates snapshots on a regular basis based on automatic snapshot policies.	N/A
Delete automatic snapshots	Automatic snapshots can be deleted automatically or manually. Automatically When the retention period specified in the associated automatic snapshot policy for an automatic snapshot ends, the snapshot is deleted. If the maximum number of automatic snapshots has been reached, the oldest automatic snapshot is deleted when a new automatic snapshot is created. After Delete Automatic Snapshots While Releasing Disk is enabled for a disk, the automatic snapshots of the disk are deleted when the disk is released. Manually Manually delete an automatic snapshot. Manually deleting a snapshot does not affect the creation of automatic snapshots based on the policy.	Delete automatic snapshots while releasing a disk ModifyDiskAttribute Delete a snapshot DeleteSnapshot
Delete an automatic snapshot policy	You can delete an automatic snapshot policy that you no longer need. After you delete an automatic snapshot policy, the policy no longer takes effect on all disks to which the policy was applied.	Delete an automatic snapshot policy DeleteAutoSnapshotPolicy

Differences between automatic snapshots and manual snapshots

Automatic and manual snapshots are point-in-time full backups of disks. They differ in the following ways:

Different creation methods
- Automatic snapshots are created based on automatic snapshot policies. After you create an automatic snapshot policy and apply the policy to a disk, the system automatically creates snapshots for the disk based on the time point or interval specified in the snapshot policy. For more information, see Create an automatic snapshot policy.
- Manual snapshot are created manually. On the Snapshots or Disks page, you can manually create a snapshot for the disk based on your business requirements. For more information, see Create a snapshot for a disk.
Different Creation Method values in console
View automatic and manual snapshots in the snapshot list:
- The Creation Method of an automatic snapshot is Automatically Created.
- The Creation Method of a manual snapshot is Manually Created.
Different names
- The name of an automatic snapshot starts with auto2.0. The naming format is auto2.0_yyyyMMdd_SnapshotPolicyId.
  - auto2.0: the prefix of the name of an automatic snapshot.
  - yyyyMMdd: the date on which the snapshot is created. yyyy stands for the year, MM for the month, and dd for the day.
  - SnapshotPolicyId: the ID of the automatic snapshot policy based on which the snapshot is created.
- The name of a manual snapshot specified when the snapshot is created.