Terms and usage scenarios of snapshots - Elastic Compute Service

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.

Important

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 using 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.

Note

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

Snapshots use data blocks as the basic unit for data backup. A data block is the fundamental unit for managing data in a storage system. The first standard snapshot of a disk is a full snapshot, which backs up all data blocks on the disk. Subsequent standard snapshots are incremental. Incremental snapshots back up only the data blocks that have changed since the previous snapshot was created. This method saves storage space and reduces 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 not visible to you. For data security reasons, you cannot currently use your own OSS buckets to store snapshots.

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 zone-redundant storage bucket.

Note

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 types

By default, disk snapshots are standard snapshots. You can archive standard snapshots. Then, the standard snapshots are moved to the archive tier and converted to archive snapshots. The following table describes the differences between standard snapshots and archive snapshots.

Item	Standard snapshot	Archive snapshot
Scenario	Suitable for daily data protection scenarios, such as temporary data backup and creation of cloud disks from snapshots for service distribution.	Suitable for scenarios in which data is infrequently used and require long-term storage, and storage costs are a concern.
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 the snapshots that are shared to you.
Snapshot replication and encryption	Supported.	Not supported.
Retention period	1 to 65,536 days Permanently Note If your Alibaba Cloud account has overdue payments, your Snapshot service is affected. For more information, see Overdue payments.	The retention period of snapshots consists of the following periods: Standard tier retention period: specifies how long standard snapshots are retained. Its value cannot be changed. A snapshot can be archived only after being retained at the standard tier for at least 14 days. Archive tier retention period: specifies how long archive snapshots are retained. Valid values: 60 to (65,536 days - Standard tier retention period) Permanently Note If your Alibaba Cloud account has overdue payments, your Snapshot service is affected. For more information, see Overdue payments.
Fee	Unit prices: View the unit prices of standard snapshots on the Pricing tab of the Elastic Compute Service product page. Billable items: You are charged standard snapshot storage fees based on the size and usage duration of standard snapshots. For more information, see Snapshots.	Unit prices: View the unit prices of archive snapshots on the Pricing tab of the Elastic Compute Service product page. Billable items: You are charged archive snapshot storage fees based on the size and usage duration of archive snapshots. Important The minimum retention period for an archive snapshot is 60 days (1,440 hours). If you delete an archive snapshot before its 60-day minimum retention period ends, you will be charged for the remaining portion of the retention period. For more information, see Snapshots.

Snapshot functionality

The following figure shows the common snapshot operations that you can perform during the lifecycle of a snapshot.

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. Manually create standard snapshots. You can manually create standard snapshots for a single cloud disk. To ensure backup data consistency, you can manually create snapshots for multiple cloud disks on one or more ECS instances at the same time by creating a snapshot-consistent group. Automatically create standard snapshots. You can create and associate an automatic snapshot policy with cloud disks to automatically create snapshots for the cloud disks based on the policy.	Manually create standard snapshots. Create a snapshot Create a snapshot-consistent group Automatically create standard snapshots. Create an automatic snapshot policy Configure an automatic snapshot policy for a cloud disk
Use a snapshot	Copy a snapshot	You can copy snapshots from one region to another region to back up data across regions.	Copy a snapshot
	Archive a snapshot	You can convert standard snapshots that you do not need to access frequently but need to retain for an extend period of time to archive snapshots to reduce snapshot storage costs.	Archive a snapshot
	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.	Share a snapshot
	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. You can use a snapshot to roll back a cloud disk. You can use a snapshot-consistent group to roll back multiple cloud disks at the same time.	Roll back a disk by using a snapshot Roll back disks by using a snapshot-consistent group
	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 a disk from a snapshot
	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 custom image from a snapshot
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.	Delete a snapshot Delete a snapshot-consistent group

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.
To reduce storage costs, you can archive standard snapshots to convert them to archive snapshots. Alibaba Cloud charges storage fees for archive snapshots based on the size and storage duration (billable duration) of the snapshots in each region.
Important
The minimum retention period for an archive snapshot is 60 days (1,440 hours). If you delete an archive snapshot before its 60-day minimum retention period ends, you will be charged for the remaining portion of the retention period.
If you use the snapshot replication feature to copy a standard snapshot from one region to another region, you are charged a data transfer fee for the snapshot replication and a storage fee for the standard snapshot copy in the destination region. Archive snapshots cannot be copied.

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
Snapshot quotas	A limited number of snapshots can be retained for each cloud disk. Up to 256 manual standard snapshots can be retained for each cloud disk. Up to 1,000 automatic standard snapshots can be retained for each cloud disk. Up to 10,000 archive snapshots can be retained for each cloud disk. Up to 100 automatic snapshot policies can be retained per region per account. One automatic snapshot policy can be associated with each cloud disk. Maximum number of concurrent snapshots per disk (including manual snapshots, automatic snapshots, snapshots in snapshot-consistent groups, and snapshots created for images) Enterprise SSD (ESSD) series disks (ESSDs, ESSD AutoPL disks, ESSD Entry disks, and Regional ESSDs): 10 Legacy disks (standard SSDs, ultra disks, and basic disks): 1
Categories of block storage devices	You cannot create snapshots for local disks or elastic ephemeral disks. Only ESSD series disks (ESSDs, ESSD AutoPL disks, and ESSD Entry disks) for which the multi-attach feature is disabled support the snapshot-consistent group feature. For information about the multi-attach feature, see Multi-attach for cloud disks. Only ESSD series disks (ESSDs, ESSD AutoPL disks, ESSD Entry disks, and Regional ESSDs) support the IA feature. For more information, see Use the instant access feature.
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: ESSD series disks (ESSD, ESSD AutoPL, ESSD Entry, and ESSD zone-redundant disks) A single disk supports the concurrent creation of manual and automatic snapshots. However, the number of concurrent snapshots that can be created is limited. For more information, see Snapshot limits. If the number of concurrent snapshots that are being created for a disk reaches the upper limit, subsequent snapshot creation tasks fail. Previous generation disks (standard SSDs, ultra disks, and basic disks) Concurrent creation of manual and automatic snapshots is not supported. At the point in time when an automatic snapshot is scheduled to be created, if a snapshot (manual or automatic) is being created for the disk, the system does not create an automatic snapshot at this point in time. An automatic snapshot is created at the next scheduled point in time. If an automatic snapshot is being created for a disk, you must wait for the automatic snapshot to be created before you can manually create a snapshot. Note For information about the differences between manual and automatic snapshots, see the Differences between automatic snapshots and manual snapshots section of the "Automatic snapshot policy" topic.

FAQ

To get answers to frequently asked questions about how to use snapshots, see Snapshot FAQ.