Why Is Snapshot Protection Still Needed When CBS Already Uses a Triple-Replica Mechanism to Protect Data Security?
When data exceptions occur at the logical layer, such as accidental data deletion by users, data corruption caused by system virus infection, or file system exceptions, the actual stored three data replicas will be modified simultaneously, making it impossible to recover normal historical data. If snapshots have been created at historical time points, you can use these snapshots to restore the data to its normal state at that historical time point.
For example, the administrator created a snapshot A for a cloud disk at 11:00, and the cloud disk was infected by a virus at 12:00, making the data unusable. At this point, the data on the three replicas had also been updated to state 2, making data recovery impossible. Only by using the snapshot A created at 11:00 can the data be restored to the uninfected state 1.
What is the difference between the snapshot and image? What is the connection between the two?
Difference between the snapshot and image
For example, if no data disk is mounted to an instance and all data is written to the system disk, the system disk cannot be protected by only creating an image. Because the image cannot be created regularly, if the system disk data is damaged, it can only be traced back to the initial data when the image was created, which cannot protect the data. The detailed differences are shown in the following table:
| Name | Snapshot | Mirror |
|---|---|---|
| Nature | A backup of cloud disk data at a certain point | Template of Cloud Virtual Machine (CVM) software configuration (operating system, pre-installed program, etc.) |
| Applicable Scenario | - Regularly back up the important business data - Back up data before major operations - Produce multi-replica application of data |
- Back up system that does not change in the short term. - Deploy applications in batch - Migrate System |
Connection Between the Snapshot and Image
- The underlying data storage of the image uses the CBS snapshot service, and the associated snapshot generated by the custom image is charged according to the actual capacity of the snapshot. You can view the total capacity of the snapshot in Snapshot Overview.
- An image is bound to its associated snapshot. To delete the associated snapshot, click Delete Image first. You can view the snapshot information associated with a custom image in Image Details.
- Snapshots can be created in both system disk and data disk. However, you can only use the system disk snapshot to create a custom image, and then use the created image to create one or more instances with the same environment.
- When a shared image is used, only the creator account of the image needs to pay for the associated snapshot, and the sharee does not need to pay.
What is the Regular Snapshot?
A scheduled snapshot is a snapshot automatically created by the system for a cloud disk associated with the scheduled snapshot policy you created. To use this feature, you need to first create a scheduled snapshot policy and associate it with a cloud disk. For specific operations, see Scheduled Snapshots.
Are There Any Regional Limits on the Snapshot?
All availability zones are supported by the current snapshot feature.
Do I Need To Uninstall Hard Disks or Interrupt All Read/Write Operations To Create Snapshots?
No. You can create snapshots in real time while the cloud disk is connected and in use, without affecting your normal business. However, snapshots can only capture data that has been written to the cloud disk and do not include data cached in memory by applications or the operating system. To ensure that all application data is captured in the snapshot, it is recommended that you completely suspend I/O operations on the hard disk before creating the snapshot. For cloud disks used as system disks, it is recommended that you shut down the CVM before creating a snapshot to create a more complete snapshot.
Does Creating Snapshots Affect the Performance of the Hard Disk?
Creating a snapshot consumes a small amount of I/O on the cloud disk. It is recommended to perform snapshot operations during relatively idle business periods.
How Long Does It Take To Create a Snapshot Until the Snapshot Become Available?
The time taken to create a snapshot is affected by various factors such as the amount of data written to the cloud disk and the underlying read-write conditions, making it difficult to predict. However, creating a snapshot does not affect the normal operation of the hard disk.
How to Create a Cloud Disk from Snapshots?
For specific operations, see Creating a Cloud Disk from a Snapshot.
How To Roll Back a Snapshot?
For specific operations, see Rolling Back Data from a Snapshot.
Do I Need To Shut Down for Snapshot Rollback?
- For a cloud disk that is already attached to a CVM, the CVM needs to be shut down before performing the rollback.
- For a cloud disk that is not attached to a CVM, you can directly perform the rollback operation.
Can a Cloud Disk Be Restored by Reading a Previous Snapshot?
Yes. You can use an existing snapshot at any point in time to restore data, regardless of the snapshot time.
Can the Source Snapshot Be Deleted When It Is Copied?
Not supported. You can delete it only after the copy is complete.
Does the Previous Disk Association Still Exist After the Copy Is Completed?
After the cross-regional copy, there will be no association between the new snapshot and the source disk of the source snapshot, and the rollback feature of the new snapshot is unavailable after copying.
How Do I Delete a Snapshot?
- Snapshots on the CBS can be deleted directly in the console or through API. For specific operations, see Delete Snapshot.
- For the associated snapshot of a custom image, you need to delete the custom image before deleting the snapshot.