This topic provides answers to frequently asked questions about Elastic Compute Service (ECS) snapshots.

If I have activated OSS, are snapshots automatically saved to my existing OSS buckets?

No, snapshots are not automatically saved to existing OSS buckets. Snapshots are stored independently from OSS buckets that you created. You do not need to create OSS buckets for snapshots.

Can a custom image that was created from a snapshot be saved to an OSS bucket?

Yes, you can export a custom image to your OSS bucket for future download. For more information, see Export a custom image. However, custom images cannot be saved directly to OSS buckets.

I have purchased an OSS resource plan and I use the snapshot and OSS services. To which service is the resource plan preferentially applied?

OSS resource plans are preferentially applied to the service whose bill is generated first. No rules exist for service priority.

What are the differences between OSS resource plans and storage capacity units (SCUs)?

  • OSS resource plans: subscription resource plans, which include storage plans and data transfer plans. You can purchase OSS Standard locally redundant storage (LRS) plans to offset your snapshot storage fee. If the storage usage exceeds the quota of the plans, the pay-as-you-go billing method is used. For more information, see Overview.
  • SCUs: subscription resource plans that can be used to offset bills for multiple pay-as-you-go storage resources, such as disks, OSS buckets, Apsara File Storage NAS file systems, and snapshots. After you purchase an SCU, the SCU is automatically used to offset the subsequent bills generated for pay-as-you-go snapshots. For more information, see Storage capacity units.

If you purchase both OSS resource plans and SCUs, the OSS resource plans are preferentially applied to offset snapshot storage fees. If the storage usage exceeds the quota of the OSS resource plans and SCUs, the pay-as-you-go billing method is used. To reduce snapshot costs, you can combine OSS resource plans and SCUs to offset snapshot storage fees.

Why am I unable to use purchased OSS resource plans to offset snapshot fees?

OSS provides various types of resource plans, such as storage plans and data transfer plans. You can use only OSS Standard LRS plans to offset snapshot storage fees. When you purchase an OSS resource plan, choose a resource plan type based on your business requirements. For more information, see Overview.

Why am I still charged for snapshots after I purchased OSS resource plans?

  • OSS resource plans can be used to offset only snapshot storage fees and cannot be used to offset data transfer fees for snapshot replication and service fees for instant access.
  • If the storage usage exceeds the quota of the OSS resource plans, the pay-as-you-go billing method is used.
For more information, see Snapshots.

What billing method is used for snapshots?

Snapshot fees include snapshot storage fees, data transfer fees for snapshot replication, and service fees for instant access. By default, you are charged snapshot fees on a pay-as-you-go basis. OSS storage plans and SCUs can be used to offset the pay-as-you-go bill of snapshot storage fees. For more information, see Snapshots.

For information about snapshot prices for different Alibaba Cloud regions, visit the Elastic Compute Service product page.

Where can I view the prices of snapshots in different Alibaba Cloud regions?

Snapshots are billed on a monthly basis. The price per GB for snapshot storage is the same as that for the OSS Standard storage class. For information about the prices of snapshots for different Alibaba Cloud regions, visit the Elastic Compute Service product page. On the page, click the Pricing tab and scroll down to the Snapshot tab. You can view region-specific snapshot prices in the Snapshot service fee details section. Download price

How can I view snapshot bills?

You can go to the User Center to view the bills and consumption details of your ECS resources. For more information, see View billing details.

What is the impact of overdue payments on snapshots?

The snapshot service is disabled after your payment becomes overdue. The length of time that your payment becomes overdue determines whether snapshots are retained. For more information, see Impacts of overdue payments.

How can I reduce snapshot costs?

  • You can use various methods to reduce snapshot costs. For example, you can maintain an appropriate number of snapshots, delete snapshots that are no longer needed, or disable unnecessary automatic snapshot policies. For more information, see Reduce snapshot fees.
  • We recommend that you purchase storage capacity units (SCUs) to offset snapshot storage fees. For more information about SCUs, see Storage capacity units.

Does the snapshot service provide a free tier?

Alibaba Cloud provides a free quota of 5 GB for snapshot storage. Snapshot storage beyond the quota is billed. For more information about snapshot billing, see Snapshots.

Am I charged for activating the snapshot service?

No, you are not charged for merely activating the snapshot feature. After you create snapshots, you are charged for the amount of storage space consumed by created snapshots.
  • For more information about snapshot billing, see Snapshots.
  • For more information about how to activate the snapshot service, see Activate ECS Snapshot.

Am I charged for using automatic snapshot polices?

No, you are not charged for merely the use of automatic snapshot polices. However, you are charged for created snapshots. Both automatic snapshots and manual snapshots incur charges.
  • For more information about snapshot billing, see Snapshots.
  • For more information about automatic snapshots, see Overview.

Am I charged for using snapshot-consistent groups?

No, you are not charged for using snapshot-consistent groups but snapshots contained in snapshot-consistent groups are billed based on the amount of storage space that the snapshots consume. If the instant access feature is enabled, you must pay both snapshot storage fees and service fees for instant access.

Do automatic snapshots differ from or conflict with manual snapshots?

No, both automatic snapshots and manual snapshots are essentially a data file that captures the point-in-time status of a disk. However, you cannot create a manual snapshot for a disk while an automatic snapshot is being created for the disk. You must wait until the automatic snapshot is created.

Can I create snapshots for local disks?

No, snapshots cannot be created for local disks. To improve the availability of applications, we recommend that you implement data redundancy at the application layer or create deployment sets for instances.

I have created a snapshot for an encrypted data disk and generated an image, but I cannot share the image, why? How can I share the image?

To ensure data privacy, custom images created from encrypted snapshots cannot be shared. We recommend that you use unencrypted snapshots to create custom images so that you can share the images with other users.

How do I view snapshot sizes?

Is the storage space released when I delete files from an ECS instance?

No, the storage space is not released when you delete files from an ECS instance. When you delete files from an ECS instance, only delete tags are added to the headers of the files. The storage space that is occupied by the disks is not reduced.

Why is the size of a snapshot greater than the disk capacity that is displayed in the file system?

  • Problem description: After you delete files from an ECS instance and create a snapshot for the instance, the size of the snapshot may not be reduced or may be greater than the disk capacity that is displayed in the file system.
  • Cause analysis: When a snapshot is being created, the system identifies empty blocks to reduce the size of the snapshot. However, some empty blocks are filled due to various processes, such as formatting the file system, deleting files, or writing data. In this case, the snapshot size may be greater than the disk capacity that is displayed in the file system. Possible causes:
    • File system metadata occupies disk space.
    • Logical Block Addressing (LBA) is used to split disks into blocks that have the same sizes. When the file system is initialized, data is written to a large number of blocks. The write operation also occupies disk space.
    • To reduce resource consumption, the file system only adds delete tags to the headers of files instead of deleting the data when you delete the files. The disk cannot detect the delete operation, and the system allocates the data blocks and copies the blocks to the snapshot. As a result, the size of the snapshot exceeds the disk capacity that is displayed in the file system.
    • Kernel-based Virtual Machine (KVM) virtio block and Xen block front modules do not support the TRIM command. The TRIM command informs a disk which data blocks in the LBA range are no longer used and can be erased. In this case, the disk cannot determine whether the data can be deleted.

What is the relationship between a file system and a disk or a snapshot?

You can create a file system in a disk partition. The file system manages disk space. These management tasks take the form of I/O requests in the disk. The disk records the status of data blocks and copies data to OSS buckets. Snapshots are created in this process. The following figure shows the relationship between a file system and a snapshot.Relationship between a file system and a disk or a snapshot
Note The preceding figure indicates that if data has been written to data blocks, the snapshot records the blocks regardless of whether the related files have been deleted from the disks. In the file system, when you delete files, only tags are added to the headers of the files, but the disk space used by the files is not released on the disks.

How can I prevent snapshots from being deleted by Alibaba Cloud?

  • Manual snapshots are never deleted by Alibaba Cloud regardless of whether the corresponding disks or instances have been released.
  • To prevent automatic snapshots from being deleted, you can modify the corresponding automatic snapshot policy by setting Retention Period to Until Deleted. After the maximum number of automatic snapshots for a disk is reached, the earliest snapshot is deleted when a new snapshot is created. For more information, see Modify an automatic snapshot policy. For more information about the snapshot quota, see Limits.

How do I stop the billing of snapshots?

If you no longer need snapshots, you can delete them to prevent further charges.

  1. Delete all snapshots, including automatic snapshots, manual snapshots, and snapshot copies. For more information, see Delete a snapshot.
  2. After existing snapshots are deleted, check if any automatic snapshot policies are being applied. If yes, delete the policies to ensure that no snapshots are created automatically. For more information, see Delete an automatic snapshot policy.

An automatic snapshot is created for a disk of an instance. Will the snapshot be deleted after the system disk of the instance is changed, the instance expires, or the disk is released?

  • If Delete Automatic Snapshots While Releasing Disk is selected for the automatic snapshot policy, automatic snapshots are deleted when the corresponding instance or disk is released.
  • If Delete Automatic Snapshots While Releasing Disk is not selected for the automatic snapshot policy, automatic snapshots are retained for the period of time specified by the automatic snapshot policy. You can modify the automatic snapshot policy. For more information, see Modify an automatic snapshot policy.

How can I delete snapshots that have been used to create images and disks?

  • You can delete snapshots that have been used to create disks. After a snapshot is deleted, operations that require the original snapshot data, such as re-initializing the system disk cannot be performed. For more information, see Reinitialize a system disk.
  • If a snapshot has been used to create custom images, you must delete those custom images before you can delete the snapshot.
  • You can delete images that have been used to create instances. After an image is deleted, operations that require the original snapshot data, such as re-initializing the system disk cannot be performed. For more information, see Reinitialize a system disk.

If I have used an automatic snapshot to create a custom image or a disk, does the automatic snapshot policy fail to be executed?

No, the automatic snapshot policy can be executed.

Can I create multiple automatic snapshot policies for a disk?

No, you cannot create multiple automatic snapshot policies for a disk. For more information, see Create an automatic snapshot policy.

If I set Retention Period to Until Delete when I created an automatic snapshot policy, can I delete snapshots created by using the policy?

Yes, you can directly delete snapshots created by using the policy. Alternatively, you can modify the retention period of snapshots created by using the policy. For more information, see Modify an automatic snapshot policy.

How can I prevent data loss caused by accidental operations?

You can create snapshots to back up data before you perform high-risk operations. For example, you can create snapshots if you want to modify critical system files, migrate instances from the classic network to a virtual private cloud (VPC), back up data, or restore an instance that was accidentally released. You can also create snapshots to recover from network attacks, change operating systems, or provide data support for a production environment. If an error occurs, you can use snapshots to roll back disks to reduce risks. For more information, see Create a snapshot of a disk and Roll back a disk by using a snapshot.

After I change the system disk of an instance, can I use a snapshot of the previous system disk to roll back the new system disk?

No, you cannot use a snapshot of the previous system disk to roll back the new system disk.

I created Instance A in the China (Hangzhou) region and created snapshots for the data disks of Instance A. After Instance A expired and was released, I created Instance B in the China (Hangzhou) region. Can I use the data disk snapshots of Instance A to restore Instance A?

No, you cannot use the data disk snapshots of Instance A to restore the Instance A after Instance A is released. If you want to use disk snapshots to restore an instance, you must make sure that the instance for which the snapshots are created is not released. To restore the data of Instance A, you can use the data disk snapshots of Instance A to create disks and attach the disks to Instance B. For more information, see Create a disk from a snapshot and Attach a data disk.

Why cannot snapshots of an instance be used to roll back the disks of the instance?

You can check the snapshots based on the returned error message. For more information about the common issues and corresponding solutions, see FAQ.

What are the differences and connections between snapshots and images?

Snapshots and images have the following relationships:
  • When you create a custom image from an instance, ECS creates a snapshot for each disk of the instance. The created custom image consists of the snapshots of all the disks of the instance. For more information, see Create a custom image from an instance.
  • You can also create custom images from system disk snapshots. For more information, see Create a custom image from a snapshot.

How do I migrate snapshots from one account to another?

Snapshots cannot be migrated across accounts. If you want to migrate a data disk snapshot in Account A to Account B, perform the following steps to create an image based on the snapshot and share the image to Account B:
  1. Create an image from the original instance to which the data disk is attached. For more information, see Create a custom image from a snapshot.
  2. Share the image to Account B. For more information, see Share a custom image.
  3. Use the image to create a pay-as-you-go instance in Account B. For more information, see Create an ECS instance by using a custom image.
  4. Create a snapshot for a data disk of the new instance. For more information, see Create a snapshot of a disk.
  5. Release the new instance. For more information, see Release an instance.

Can I use a data disk snapshot to create a custom image?

No, data disk snapshots cannot be used to create custom images. Only system disk snapshots can be used to create custom images.

Can snapshots be downloaded or exported to on-premises devices?

No, snapshots cannot be downloaded or exported to on-premises devices. You can create images from snapshots and then export the images. For more information, see Create a custom image from a snapshot and Export a custom image.

Alternatively, you can use the OOS template named ACS-ECS-BulkyCreateAndExportImage, create custom images based on one or more instances in the corresponding region, and then export the images to OSS buckets. Then, you can download the images in the OSS console.

Why does the "RequestId: xxx" error message appear when I delete a snapshot in the snapshot chain?

Your snapshot was used to create a custom image. You must delete the custom image before you can delete the snapshot. For more information, see Delete a custom image.