Snapshots provide point-in-time replicas of cloud disk data and serve as a critical component of your disaster recovery strategy. Use snapshots to back up business data stored on cloud disks at regular intervals. This protects against data loss caused by accidental operations, malicious attacks, or viruses. If data loss or corruption occurs on a cloud disk, you can restore the disk to an earlier point in time using a snapshot, ensuring business continuity.
Elastic Compute Service (ECS) instances do not automatically back up data stored on cloud disks. To reduce the risk of data loss from major O&M operations—such as configuration changes or upgrades—along with from attacks or viruses, create snapshots periodically after creating ECS instances.
Scenarios
Use Alibaba Cloud snapshots in the following scenarios.
Daily data backup
Use automatic snapshot policies to create snapshots for cloud disks at scheduled intervals and retain them for a specified period. This provides daily protection for cloud disk data against accidental operations, virus infections, or malicious attacks.
Critical Operation Protection
Before performing O&M operations on ECS instances or cloud disks—such as capacity expansion, configuration changes, or migration—manually create snapshots to back up data. If issues arise, you can quickly restore business data from these snapshots.
Fast data restoration
If your system encounters software compatibility issues during an upgrade or suffers a service interruption, roll back cloud disks using the corresponding snapshots. This restores business data rapidly and maintains business continuity.
Batch business deployment
Create custom images from snapshots and then launch ECS instances from those images. This enables efficient, large-scale deployment or upgrade of business applications across multiple sites.
Batch data distribution
Create multiple new cloud disks from a single snapshot and attach them to ECS instances as needed. This distributes business data quickly and efficiently.
Snapshots back up individual disks or disk groups. To simultaneously back up or clone all disks attached to an ECS instance, use the ECS instance backup feature of Cloud Backup.
Get started with snapshots
Working principles
Snapshots use data blocks—the fundamental unit for managing data in a storage system—as the smallest unit for backup. The first standard snapshot of a disk is a full snapshot, which copies all data blocks on the disk. Subsequent standard snapshots are incremental snapshots, which copy only the data blocks that have changed since the previous snapshot. This approach reduces storage usage and lowers costs. For more information about how snapshots work, see How snapshots work.
Storage locations
Snapshots are stored by default in Object Storage Service (OSS) to ensure long-term data security and flexible recovery. The OSS bucket used for this purpose is managed internally and is not visible to you. For security reasons, you cannot store snapshots in your own OSS buckets.
By default, snapshot data is stored in zone-redundant storage (ZRS) buckets in regions where OSS supports ZRS, maximizing 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 Object Storage Service (OSS) supports zone-redundant storage, see Storage redundancy and Create a zone-redundant storage bucket.
After creating a cloud disk or rolling back a cloud disk using a snapshot, the snapshot data loads from OSS to the cloud disk. The cloud disk prioritizes loading data that is read first. The duration of this process depends on the data volume of the snapshot and ranges from minutes to hours. During this time, read access latency for the cloud disk increases. Once all snapshot data blocks load to the cloud disk, read performance returns to normal.
Snapshot instant access
Creating and uploading a snapshot for a disk with a large amount of data takes longer. The instant access (IA) feature lets you use snapshots within seconds of creation, before they finish uploading to Object Storage Service (OSS). You can use IA snapshots to create cloud disks, roll back cloud disks, or share snapshots. For more information, see Snapshot instant access.
Snapshot data security
To meet security and compliance requirements, snapshots are encrypted during storage and backup. Snapshot encryption ensures that backups of encrypted cloud disks—including system disks and data disks—remain encrypted. Even if snapshot data is compromised, it cannot be decrypted, preserving the confidentiality and integrity of your backup data.
If a cloud disk is encrypted, its snapshots inherit the encryption attribute. Snapshot data remains encrypted during storage, transmission, cross-region copying, and restoration. For more information, see Confidentiality of data storage.
Snapshot types
Disk snapshots created on Alibaba Cloud are standard snapshots by default. You can archive a standard snapshot to convert it into an archive snapshot. The main differences between standard and archive snapshots are as follows:
Item | Standard snapshot | Archive snapshot |
Scenario | Suitable for daily data protection tasks, such as temporary data backup and creating cloud disks from snapshots for service distribution. | Suitable for infrequently accessed data requiring long-term retention, especially when storage cost optimization is a priority. |
Convertibility | Standard snapshots can be converted to archive snapshots. | Archive snapshots cannot be restored to standard snapshots. |
Disk rollback, disk creation, image creation, and snapshot sharing | Supported. | Supported. Note You can share archive snapshots, but you cannot archive snapshots shared with you. |
Snapshot replication and encryption | Supported. | Not supported. |
Retention period |
Note If your Alibaba Cloud account has overdue payments, your snapshot service is affected. For more information, see Overdue payments. | The retention period of an archive snapshot consists of two parts: the standard tier retention period (duration of standard snapshot storage) and the archive tier retention period (duration of retention after archiving).
Note If your Alibaba Cloud account has overdue payments, your snapshot service is affected. For more information, see Overdue payments. |
Snapshot fees |
For more information, see Snapshot billing. |
For more information, see Snapshot billing. |
Snapshot functionality
The following figure shows common snapshot features across the snapshot lifecycle.
Feature | Description | References | |
Create a snapshot | You can create a standard snapshot using one of the following methods:
|
| |
Use a snapshot | Copy a snapshot | Copy snapshots from one region to another to back up data across regions. | |
Archive snapshots | Archive standard snapshots that are infrequently accessed but require long-term retention to reduce storage costs. | ||
Share a snapshot | Share snapshots with other Alibaba Cloud accounts or within your organization using resource directories. Other accounts can use your shared snapshots to quickly create disks for daily O&M tasks. | ||
Roll back a cloud disk using a snapshot | If system faults occur or data is lost due to accidental operations, use snapshots to roll back cloud disks and restore data.
| ||
Create a cloud disk from a snapshot | Create a new data disk from a snapshot. The new disk contains identical data to the original disk at the time the snapshot was taken. This enables data replication within the same zone or across zones, supporting environment cloning or data backup. | ||
Create an image from a system disk snapshot | Create a custom image from a system disk snapshot. This replicates the operating system and data environment of an ECS instance. Then, use the custom image to launch multiple ECS instances, enabling rapid application environment replication. | ||
Delete a snapshot | If you no longer need a snapshot or exceed your snapshot quota, delete the snapshot to free storage space and avoid ongoing charges. | ||
Billing
You must enable the snapshot service before you can use snapshots. Enabling the snapshot service is free of charge. Billing starts only after a snapshot is created. By default, manual snapshots and snapshots created by an automatic snapshot policy are standard snapshots. Alibaba Cloud charges a standard snapshot storage fee in each region based on the standard snapshot size and storage duration.
To reduce storage costs, you can archive standard snapshots. When you archive a standard snapshot, it is converted to an archive snapshot. Alibaba Cloud charges an archive snapshot storage fee in each region based on the archive snapshot size and storage duration.
ImportantThe minimum retention period for an archive snapshot is 60 days (1,440 hours). If you delete an archive snapshot before this period ends, you are charged a fee for deleting the snapshot before the minimum retention period.
If you use the snapshot replication feature to copy standard snapshots to a destination region for cross-region data backup, you incur a snapshot replication traffic fee and a standard snapshot storage fee in the destination region. Archive snapshots cannot be replicated.
For more information about snapshot billing, see Snapshot billing.
Limits
Note the following limits when using snapshots:
Limit | Description |
Snapshot quotas |
|
Categories of block storage devices |
|
Download or export of snapshots | Downloading or exporting created snapshots is not supported. You can create custom images from snapshots and then export the custom images to a local device. |
Other limitations | Manual and automatic snapshot creation has the following constraints:
Note For information about the differences between manual and automatic snapshots, see Differences between automatic and manual snapshots. |
FAQ
For frequently asked questions about snapshots, see Data Protection and Recovery.