In situations where a logic-level data error occurs, for example, suppose a user deletes data by mistake, or if the data is damaged by a virus or file system exceptions, all three copies of the data stored will be affected and historical data cannot be restored. If you have created a snapshot previously, you can use the snapshot to restore data to the point in time the snapshot was created.
Suppose an administrator created snapshot A for a cloud disk at 11:00, and the cloud disk was infected with a virus at 12:00, which caused that data to be unusable. In this case, the three copies of the data would have been updated to state 2, and the data cannot be restored. Only snapshot A created at 11:00 can be used to restore data to the uninfected state 1.
If no data disk is mounted to an instance and all data is written on the system disk, the data on the system disk cannot be protected by creating an image. Images cannot be scheduled for continuous backup. Once the system disk data is damaged, you can only recover the data to when the image was initially created. Therefore, images are not suitable for data protection. Specific differences are as follows:
|Characteristics||Backup data of a cloud disk at a certain point in time||CVM software configuration template, contains information including the operating system and pre-installed programs|
A scheduled snapshot is automatically created by the system according to the scheduled snapshot policy you created for the cloud disk associated with the policy. To use this feature, you must first create a scheduled snapshot policy and associate it with the cloud disk.
A maximum of 30 scheduled snapshot policies can be created in one region. Each scheduled snapshot policy can be associated with up to 200 cloud disks. In addition, snapshots created according to the scheduled snapshot policies comply with snapshot quota limits. For more information, see Use Limits.
The snapshot feature is available in all availability zones.
Snapshots are billed according to your total snapshot storage capacity in each region. CBS is pay-as-you-go with an hourly billing cycle. For more information on billing, see Billing Overview and Pricing List.
No. You can create a real-time snapshot while the disk is connected and in use, without affecting normal business operation. However, the snapshot can only capture data that has been written into the cloud disk, not data cached in memory by applications or the operating system. To ensure all application data is captured, we recommend that you suspend all disk I/O operations before creating a snapshot. For a cloud disk that is used as a system disk, we recommend that you shut down the CVM to create a more complete snapshot.
Creating a snapshot will occupy a small amount of the disk I/O. We recommend creating snapshots when business is slow.
The time for creating a snapshot is subject to factors such as the number of disk writes, and the underlying read-write operations. It is hard to predict, but creating a snapshot does not affect your normal disk use.
Yes. You can use an existing snapshot created at any point in time to restore data, regardless of the snapshot’s point in time.
No. It can only be deleted after the replication is complete.
After cross-region replication, the new snapshot is no longer associated with the source disk of the source snapshot. The rollback feature is unavailable for replicated snapshot.