Snapshots are an important disaster recovery method, which provide complete point-in-time replicas of cloud disk data. To protect 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 data loss or exceptions occur on a cloud disk, you can restore the disk data to an earlier point in time by using a snapshot of the cloud disk. This ensures business continuity.
Elastic Compute Service (ECS) instances do not automatically back up data stored on cloud disks. To reduce the risk of data loss caused by major O&M operations (such as configuration changes and upgrades), 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 protect against data loss caused by accidental operations, attacks, or viruses, you can use automatic snapshot policies to periodically create automatic snapshots for cloud disks and retain the snapshots for a specific period of time.
Disaster recovery and fault tolerance
Before you perform O&M operations on ECS instances and cloud disks, such as capacity extension, configuration changes, or migration, you can manually create snapshots to back up data. This allows you to restore your business data from the snapshots.
Fast data restoration
If your system encounters a software compatibility issue during an upgrade or a service interruption occurs, you can roll back cloud disks by using the corresponding snapshots to quickly restore business data and ensure business continuity.
Batch business deployment
To batch deploy or upgrade your business on multiple sites, you can create custom images based on snapshots and then create ECS instances from the 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 are created as backups of a cloud disk or cloud disk group. To simultaneously create snapshots for all cloud 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, which includes all data stored on the cloud disk 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 cloud disk since the previous snapshot was created. This minimizes the space required to store snapshots and reduces storage costs.
Full 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 existing 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 and secure storage and flexible restoration of data, snapshots are automatically stored in 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 is not loaded, the system immediately loads the snapshot data from OSS to the cloud disk. The time required to complete the loading process varies based on the snapshot size 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 cloud disk, the read latency of the cloud disk returns to the normal level.
Instant access (IA)
A cloud disk that contains a larger amount of data requires a longer period of time to create a snapshot for the disk and upload the snapshot to OSS. The IA feature allows you to use snapshots within seconds of snapshot creation, instead of after the snapshots are fully 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 data storage and backup. 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, snapshots of the cloud disk are also encrypted. Snapshot data remains 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 snapshot operations that you can perform during the lifecycle of a snapshot.
Feature | Description | References | |
Feature | Description | References | |
Create a snapshot | You can manually or automatically create standard snapshots. Manually created standard snapshots are called manual standard snapshots. Automatically created standard snapshots are called automatic standard snapshots.
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Use a snapshot | Copy a snapshot | You can copy snapshots from one region to another region to back up data across regions. | |
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. | ||
Roll back a cloud disk by using a snapshot | If system faults occur or data is lost due to accidental operations, you can use snapshots to roll back cloud disks to restore data.
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Create a cloud disk from a snapshot | You can create a data disk from a snapshot. The data on the data disk is the same as the data on the source disk when the snapshot was created. Snapshot-based disk creation allows you to quickly replicate cloud disks in the same zone or across zones for environment cloning or data backup. | ||
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. | ||
Delete a snapshot | If you no longer require one or more snapshots or the maximum number of snapshots is reached, you can delete snapshots to free up storage space and prevent unnecessary charges. | ||
Billing
Before you can create snapshots, you must activate the Snapshot service. You are not charged for activating the Snapshot service, but you are charged for the snapshots that you create. By default, manual snapshots and automatic snapshots created based on automatic snapshot policies are standard snapshots. Alibaba Cloud charges storage fees for standard snapshots based on the size and storage duration (billable duration) of the snapshots in each region.
If you use the snapshot replication feature to copy a snapshot from one region to another region, you are charged a data transfer fee for the snapshot replication and a storage fee for the new standard snapshot (snapshot copy) in the destination region.
For more information about the billing of snapshots, see Snapshots.
Limits
When you use snapshots, take note of the limits described in the following table.
Limit | Description |
Limit | Description |
Snapshot quotas |
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Categories of block storage devices |
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Download or export of snapshots | You cannot download or export created snapshots. You can create custom images from snapshots and export the custom images to your on-premises device. |
Others | The following limits apply to manual and automatic snapshots:
For information about the differences between manual and automatic snapshots, see the Automatic snapshot policy section of the "Automatic snapshot policy" topic. |
FAQ
To obtain answers to frequently asked questions about how to use snapshots, see Snapshot FAQ.
