The Alibaba Cloud snapshot service is an agentless backup service that allows you to create crash-consistent snapshots for all disk categories to back up or restore an entire disk. Crash-consistent snapshots are an effective solution to disaster recovery and can be used to back up data, create images, and implement disaster recovery for applications.
A snapshot is a point-in-time backup of a disk. The first snapshot of a disk is a full snapshot that does not contain the copies of empty data blocks. Subsequent snapshots are incremental snapshots that store only changed data blocks. For more information, see Incremental snapshots.The following figure shows common operations on a snapshot.
|Create a snapshot||You can use the following methods to create snapshots:
|Roll back a disk||When the system is unresponsive or when accidental changes are made, you can roll back a disk to a previous version by using one of its snapshots.||Roll back a disk by using a snapshot|
|Create an image from a system disk snapshot||You can create a custom image from a snapshot that contains the operating system and data of an ECS instance. Then, you can use the custom image to create multiple instances that have identical application environments.||Create a custom image from a snapshot|
|Create a disk from a snapshot||A single snapshot can be used to create multiple identical disks.
Note You can use a snapshot to create disks across zones.
|Create a disk from a snapshot|
|Copy a snapshot from other regions||When a snapshot is copied from one region to another, a copy of the snapshot is created in the destination region.||Copy a snapshot|
- Instant access: After the instant access feature is enabled for a snapshot, the snapshot can be used to roll back disks or create disks across zones even when the snapshot is being created. For more information, see Enable or disable the instant access feature.
- Application-consistent snapshot: Application-consistent snapshots can be used to roll back applications to ensure that the applications start in a consistent state. For more information, see Create application-consistent snapshots in the ECS console.
For information about the billing of snapshots, see Snapshots.
For information about the limits and quotas of snapshots, see the "Snapshot limits" section in Limits.
- 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 ECS instances that have identical environments.
- Improvement of fault tolerance: You can reduce the risk of data loss caused by accidental
changes by using a snapshot to roll a disk back to a previous version. Snapshots are
suitable for the following scenarios:
- Create snapshots on a regular basis to prevent data loss caused by accidental changes or external attacks. For example, data may be lost due to the fact that invalid data is written to disks, ECS instances are accidentally released, data errors arise from application errors, or hackers exploit application vulnerabilities to delete business data.
- Create snapshots before you perform high-risk O&M operations, such as replacing operating systems, upgrading applications, and migrating data.
|Item||Alibaba Cloud ECS snapshot||Traditional storage service snapshot|
|Capacity||Unlimited capacity for storing large amounts of business data.||Limited capacity, dependent on the capacity of the storage device.|
|Scalability||High scalability allows you to extend storage devices to any size within seconds.||Low scalability, dependent on the storage performance, available capacity, and vendor support.|
|Total cost of ownership (TCO)||You need only to pay for the amount of storage space occupied by your snapshots.||High upfront costs for software licenses, reserved storage space, upgrade, and maintenance.|
|Security||Supports data encryption. After you encrypt a disk, all snapshots that are created for it are also encrypted. Unencrypted snapshots cannot be converted to or from encrypted snapshots. For more information, see Encryption overview.||Encryption attributes and policies are subject to the underlying storage logic. If the storage architecture has security flaws, snapshots created based on this architecture may also have security flaws.|
|Impacts on performance||Uses redirect-on-write (ROW).
||Typically uses copy-on-write (COW), but may also use ROW or other methods. COW may affect the data write capabilities of the source system.|