Snapshots provide complete point-in-time replicas of cloud disk data and are an important method for disaster recovery. To mitigate against data loss caused by accidental operations, attacks, or viruses, you can use snapshots to periodically back up business data stored on cloud disks. If a cloud disk suffers data loss or exceptions, you can use a snapshot of the cloud disk to restore disk data to an earlier point in time. This ensures business continuity.
Elastic Compute Service (ECS) instances do not automatically back up data stored on cloud disks. To eliminate the risk of data loss caused by major O&M operations (such as configuration change and upgrade), attacks, or viruses, we recommend that you create snapshots on a periodical basis to back up cloud disk data after you create ECS instances.
Scenarios
We recommend that you use snapshots in the following scenarios:
Daily data backup
To back up cloud disk data and mitigate against data loss caused by accidental operations, attacks, or viruses, you can use automatic snapshot policies to create automatic snapshots for cloud disks on a periodical basis and retain the snapshots for a specific period of time.
Disaster recovery and fault tolerance
Before you perform O&M operations (such as capacity extension, configuration change, and migration) on ECS instances and cloud disks, you can manually create snapshots to back up data. This way, you can restore your business data from the snapshots when required.
Fast data restoration
If your system encounters a software compatibility issue during an upgrade or suffers a service interruption for any other reason, you can roll back cloud disks by using their snapshots to quickly restore business data and ensure business continuity.
Batch business deployment
To batch deploy or upgrade your business on multiple sites in an efficient manner, you can create custom images based on snapshots and then create ECS instances from the custom images.
Batch data distribution
To quickly distribute business data, you can batch create cloud disks from snapshots and attach the cloud disks to ECS instances based on your business requirements.
Snapshots can be used to create backups of a disk or disk group. To simultaneously create snapshots for all disks on an ECS instance to back up or clone the instance, use the ECS instance backup feature of Cloud Backup.
Get started with snapshots
Working principles
Alibaba Cloud snapshots provide full or incremental backups of data stored on cloud disks. The first snapshot that you create for a cloud disk is a full snapshot. This snapshot includes all data stored on the cloud disk at the time when the snapshot is created. Subsequent snapshots of the same cloud disk are incremental snapshots. These snapshots include only the data added or changed on the disk since the previous snapshot was created. This minimizes the amount of space required to store snapshots and saves on storage costs.
The full snapshot and incremental snapshots include information about all data blocks on the cloud disk. When you roll back the cloud disk by using a snapshot, you can restore cloud disk data to the point in time when the snapshot was created. After you delete a snapshot of the cloud disk, you can use an undeleted snapshot of the cloud disk to restore cloud disk data to the point in time when the snapshot was created. For more information about the working principles of snapshots, see How snapshots work.
Storage locations
To ensure long-term, secure storage, and flexible restoration of data, snapshots are automatically stored in Alibaba Cloud Object Storage Service (OSS). For data security reasons, you cannot select the OSS buckets that you created to store snapshot data.
By default, snapshot data is stored in zone-redundant storage (ZRS) buckets in regions where OSS supports ZRS to maximize data redundancy.
In regions where OSS does not support ZRS, snapshot data is stored in locally redundant storage (LRS) buckets. If your business requires high availability, we recommend that you copy snapshots to back up data across regions.
For information about the regions where OSS supports ZRS, see Storage redundancy and Create a ZRS bucket.
After you use a snapshot to create or roll back a cloud disk, the data contained in the snapshot is loaded from OSS to the cloud disk. If you access the snapshot data that has not been loaded, the system immediately loads the snapshot data from OSS to the cloud disk. The amount of time required to complete the loading process varies based on the size of the snapshot and could be minutes or hours. Before all data contained in the snapshot is loaded to the cloud disk, the read latency of the cloud disk increases. When all data contained in the snapshot is loaded to the disk, the read latency of the cloud disk returns to the normal level.
Instant access
A larger amount of data on a disk requires a longer period of time to create a snapshot for the disk and upload the snapshot to OSS. The instant access (IA) feature allows you to use snapshots within seconds of snapshot creation, instead of after the snapshots are completely uploaded to OSS. You can use IA snapshots to perform various operations, such as creating cloud disks, rolling back cloud disks, and sharing snapshots. For more information, see Use the instant access feature.
Snapshot data security
To meet security and compliance requirements, we recommend that you encrypt snapshots during the data storage and backup processes. Snapshot encryption ensures that data backups of encrypted cloud disks (including system disks and data disks) are encrypted. Encrypted snapshot data cannot be decrypted and remains confidential and integral even if data leaks occur.
If a cloud disk is encrypted, its snapshots inherit the encryption attribute of the cloud disk, which allows the snapshot data to remain encrypted during storage or transmission. The snapshot data remains encrypted even if the snapshots are copied to another region or used to restore the cloud disk. For more information, see the Confidentiality of data storage section of the "Data security" topic.
Snapshot functionality
The following figure shows the common features provided by snapshots.
Feature | Description | References |
Create a snapshot | You can use the following methods to create snapshots:
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Roll back cloud disks | If system faults occur or data is lost due to accidental operations, you can use snapshots to roll back cloud disks to restore data. You can use a snapshot to roll back a single disk or use a snapshot-consistent group to roll back one or more cloud disks. | |
Create an image from a system disk snapshot | If you have a snapshot of the system disk of an ECS instance, you can create a custom image from the snapshot. The custom image includes the instance operating system and data captured in the snapshot. You can use the custom image to create multiple instances that have identical application environments. | |
Create a cloud disk from a snapshot | You can create cloud disks from a snapshot to quickly replicate disks within the same zone or across zones. | |
Share a snapshot | You can share snapshots with other Alibaba Cloud accounts or within your organization based on resource directories. Other Alibaba Cloud accounts can use your shared snapshots to quickly create disks to meet daily O&M requirements. | |
Copy a snapshot | You can copy snapshots from one region to another region to back up data across regions. |
Billing
You must activate the Snapshot service before you can create snapshots. For more information, see Activate ECS Snapshot. You can activate the Snapshot service free of charge. You are charged only for the snapshots that you create.
By default, snapshots created for cloud disks are standard snapshots. Alibaba Cloud charges storage fees for standard snapshots based on the size and storage duration of the snapshots. For information about the billing of snapshots, see Snapshots.
NoteIf you use an automatic snapshot policy or a snapshot-consistent group to create snapshots, you are not charged for the automatic snapshot policy or the snapshot-consistent group but are charged for the snapshots.
If you copy a snapshot across regions. you are charged a storage fee for the snapshot in the source region, a data transfer fee for copying the snapshot, and a storage fee for the snapshot copy in the destination region. For information about the billing of snapshots, see Snapshots.
Limits
Item | Description |
Snapshot quotas |
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Cloud disk categories |
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Local disks and elastic ephemeral disks | Local disks and elastic ephemeral disks do not support manual snapshots, automatic snapshots, or snapshot-consistent groups. |
IA | Only ESSD-series disks (ESSDs, ESSD AutoPL disks, and ESSD Entry disks) support the IA feature. |
Download or export of snapshots | You cannot download or export snapshots. You can create custom images from snapshots and then export the custom images to your on-premises device. |
FAQ
For the frequently asked questions about how to use snapshots, see Snapshot FAQ.