The Alibaba Cloud snapshot service allows you to create crash-consistent snapshots for all disk categories. Crash-consistent snapshots are an effective solution to disaster recovery and are used to back up data, create custom images, and implement disaster recovery for applications.

Scenarios

You can use snapshots for the following scenarios:
  • Disaster recovery and backup: You can create a snapshot for a disk, and then use the snapshot to create another disk to implement zone- or geo-disaster recovery.
  • Environment clone: You can use a system disk snapshot to create a custom image, and then use the custom image to create an ECS instance to clone the environment.
  • Data development: Snapshots can provide near-real-time production data for applications such as data mining, report queries, and development and tests.
  • Enhanced fault tolerance: You can roll a disk back to a previous point in time by using a snapshot to reduce the risk of data loss caused by unexpected occurrences. You can create snapshots in the following cases:
    • Create snapshots on a regular basis to prevent losses caused by unexpected occurrences. These unexpected occurrences include: writing incorrect data to disks, accidentally releasing ECS instances, data errors caused by application errors, and data loss due to hacking attempts.
    • Create a snapshot before you perform high-risk O&M operations, such as changing operating systems, upgrading applications, and migrating business data.

Snapshot classification

Snapshots include normal and local snapshots. Snapshots are classified based on how they are stored. The following table describes the classification of snapshots based on different standards.

Classification standard Type Description Scenario
Storage method Normal snapshot

A snapshot is stored in an OSS bucket that resides in the same region as the disk for which the snapshot is created. You can create normal snapshots for disks . Normal snapshots can be created for system disks and data disks.

Normal snapshots are applicable to scenarios that require high disaster recovery capabilities. However, it takes a long time to create normal snapshots.
Local snapshots

A local snapshot is stored in the same storage cluster as the disk for which the snapshot is created and can be used to perform data backup and disk rollback within a few seconds. Local snapshots can be created only for enhanced SSDs (ESSDs).

  • You can use local snapshots to quickly back up key business systems that contain huge data, such as databases, containers, and SAP HANA.
  • You can also use local snapshots to quickly back up data before you perform high-risk operations. High-risk operations include changing system disks, resizing disks, and updating system patches.
  • You can use local snapshots in DevOps applications to accelerate the creation of custom images and the startup of ECS instances.
Creation method Manual snapshot

A manual snapshot is a snapshot that you manually create.

You can create a manual snapshot before you perform high-risk operations to enhance fault tolerance.
Automatic snapshot
An automatic snapshot is a snapshot that is created automatically based on an automatic snapshot policy. You can create and apply an automatic snapshot policy to a disk. Then, ECS automatically creates snapshots for the disk at specified points in time.
Note All automatic snapshots are normal snapshots.
You can use automatic snapshots to back up data and improve the security of business data.
Creation order Full snapshot

A full snapshot is the first snapshot created for a disk. This snapshot contains all the data stored on the disk at the time the snapshot is created.

N/A
Incremental snapshots

An incremental snapshot is a snapshot created after the full snapshot. The snapshot contains only incremental data blocks.

N/A
Encryption Encrypted snapshot An encrypted snapshot is a snapshot created from an encrypted disk.
Note All encrypted snapshots are normal snapshots.
You can create encrypted snapshots if your business is required to comply with certain security standards.
Unencrypted snapshot An unencrypted snapshot is a snapshot created from an unencrypted disk. N/A

Billing

Snapshots are billed based on their sizes. They can be billed on a pay-as-you-go basis. For more information, see Snapshot billing.
Note Local snapshots can be billed only on a pay-as-you-go basis and cannot be offset by OSS storage plans.

Limits

For more information about the limits and quotas of snapshots, see the "Snapshot limits" section in Limits.

Local snapshots have the following limits:
  • Local snapshots can be created only for ESSDs.
  • A maximum of 10 local snapshots can be retained for an ESSD.
  • When you use a local snapshot to create a disk, the specified disk size cannot be larger than the snapshot size.
  • You cannot use automatic snapshot policies to create local snapshots.
  • Local snapshots cannot be created for encrypted disks or local disks.

Benefits

The following table describes the benefits of Alibaba Cloud ECS snapshots compared with the snapshot feature of traditional storage services.
Item Alibaba Cloud ECS snapshot Snapshot of traditional storage service
Capacity Unlimited capacity for storing large amounts of business data. Limited capacity based on the capacity of the storage device.
Scalability High scalability allows you to extend storage devices to any size within seconds. Low scalability due to limited storage performance, available capacity, and vendor support.
Total cost of ownership (TCO) Pay only for the storage space occupied by your snapshots. Pay large upfront costs for software licenses, reserved storage space, upgrade, and maintenance.
Security Support data encryption. If you encrypt your source disk, all snapshots created for the disk are encrypted. Unencrypted snapshots cannot be directly converted to encrypted snapshots, and encrypted snapshots cannot be directly converted to unencrypted snapshots. For more information, see Encryption overview. Encryption attributes and policies are subject to the underlying storage logic. If the storage architecture has a security flaw, snapshots created based on this architecture may not be secure.
Implementation method and impact on performance Redirect-on-write (ROW)
  • Reduce impacts on the I/O performance of the source disk.
  • Snapshots do not affect service availability and can be created at any time without affecting user experience.
Typically copy-on-write (COW), but probably ROW or other methods. COW negatively affects the data write capabilities of the source system.

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