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    Elastic Compute Service:Snapshot FAQ

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    Elastic Compute Service:Snapshot FAQ

    Last Updated:Nov 01, 2024

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

    Are snapshots automatically saved to my existing OSS buckets after I activate OSS?

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

    Can I export a custom image that is created from a snapshot 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, you cannot directly export custom images to OSS buckets.

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

    • OSS resource plans: subscription resource plans, including storage plans and data transfer plans. For more information, see Overview of resource plans.

    • SCUs: subscription resource plans that can be used to offset bills for multiple pay-as-you-go storage resources, such as disks, OSS buckets, File Storage NAS file systems, and snapshots. After you purchase an SCU, the SCU is automatically used to offset subsequent bills generated for pay-as-you-go snapshots. For more information, see SCUs.

    How do I restore the data of an ECS instance from snapshots after the instance is released?

    To restore the data of an ECS instance from snapshots after the instance is released, perform the following steps:

    1. Create a custom image from the snapshots that were created for the disks attached to the ECS instance. For more information, see Create a custom image from a snapshot.

    2. Create an ECS instance from the custom image. For more information, see Create an instance by using a custom image.

    3. Connect to the new ECS instance, check whether the data of the released ECS instance is completely restored, and then copy or further process the data.

      Important

      You are charged for the computing and storage resources of the new ECS instance. To prevent unnecessary fees, we recommend that you release the new ECS instance at the earliest opportunity after you restore the data of the released ECS instance.

    What billing method is used for snapshots?

    Snapshot fees may include snapshot storage fees and data transfer fees for snapshot replication. By default, you are charged snapshot fees based on the pay-as-you-go billing method. You can use SCUs to offset the pay-as-you-go bills of snapshot storage fees. For more information, see Snapshots.

    For information about the pricing of snapshots for different Alibaba Cloud regions, visit the Elastic Compute Service product page and click the Pricing tab.

    How do I view the pricing of snapshots for 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 pricing of snapshots for different Alibaba Cloud regions, visit the Elastic Compute Service product page, click the Pricing tab, and then scroll down to and click the Snapshot tab. In the Snapshot service fee details section, you can view the pricing of region-specific snapshots.

    How do I view snapshot bills?

    You can view the bills and consumption details of your ECS resources in the Expenses and Costs console. For more information, see View billing details.

    What is the impact of overdue payments on snapshots?

    The Snapshot service is deactivated after your payment becomes overdue. The duration that your payment remains overdue determines whether snapshots are retained. For more information, see the Impacts of overdue payments section in the "Snapshots" topic.

    How do I reduce snapshot costs?

    • You can retain an appropriate number of snapshots, delete snapshots that are no longer needed, and disable unnecessary automatic snapshot policies to reduce snapshot costs. For more information, see Reduce snapshot fees.

    • We recommend that you purchase SCUs to offset snapshot storage fees. For information about how to purchase SCUs, see Storage capacity units.

    Does the Snapshot service have a free quota?

    Alibaba Cloud provides a free quota of 5 GB for snapshot storage. You are charged for snapshot storage that exceeds the quota. For information about snapshot billing, see Snapshots.

    Am I charged for activating the Snapshot service?

    No, you are not charged for activating the Snapshot service. After you create snapshots, you are charged for the storage space occupied by the created snapshots.

    Am I charged for using automatic snapshot policies?

    No, you are not charged for using automatic snapshot policies. However, you are charged for the created snapshots regardless of whether the snapshots are automatically or manually created. For more information, see Snapshots.

    Am I charged for using snapshot-consistent groups?

    No, you are not charged for using snapshot-consistent groups. However, you are charged for snapshots in snapshot-consistent groups based on the storage space that is occupied by the snapshots. For more information, see Snapshots.

    What are the differences between manual snapshots and automatic snapshots?

    Automatic and manual snapshots are copies of disk data at specific points in time. Automatic and manual snapshots have the following differences:

    • Different creation methods

      • Manual snapshots are manually created. You can create snapshots for disks on the Snapshots or Block Storage (Disks) page and configure snapshot parameters based on your business requirements. For more information, see Create a snapshot.

      • Automatic snapshots are created based on automatic snapshot policies. After you create an automatic snapshot policy and apply the policy to a disk, the system automatically creates snapshots for the disk based on the points in time or interval specified in the policy. For more information, see Create an automatic snapshot policy.

    • Different values in the Creation Method column

      When you view manual and automatic snapshots in the snapshot list, the following differences exist:

      • The Creation Method value of an automatic snapshot is Automatic Snapshot.

      • The Creation Method value of a manual snapshot is Manual Snapshot.

    • Different snapshot names

      • The name of a manual snapshot is specified when the snapshot is created.

      • The name of an automatic snapshot starts with auto2.0. The name is in the auto2.0_yyyyMMdd_SnapshotPolicyId format.

        • auto2.0: the prefix of the name of an automatic snapshot.

        • yyyyMMdd: the date on which the snapshot is created. yyyy indicates the year, MM indicates the month, and dd indicates the day.

        • SnapshotPolicyId: the ID of the automatic snapshot policy based on which the snapshot is created.

    Note

    When you use manual and automatic snapshots, take note of the following limits:

    • If a snapshot is being manually or automatically created for a disk when a point in time designated in the associated automatic snapshot policy arrives, the system cannot create an automatic snapshot based on the policy at the point in time. An automatic snapshot is created for the disk at the next point in time that is designated in the automatic snapshot policy.

    • If an automatic snapshot is being created for a disk, you cannot create a manual snapshot for the disk. Wait until the automatic snapshot is created before you can manually create a snapshot.

    Can I create snapshots for local disks?

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

    I created a snapshot for an encrypted data disk and generated an image based on the snapshot. Why am I unable to share the image? How do I share the image?

    To ensure data privacy, you cannot share custom images created from encrypted snapshots. We recommend that you use unencrypted snapshots to create custom images. This way, 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 on disks that is occupied by the files is not reduced.

    Why is the size of a snapshot larger 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 larger than the disk capacity that is displayed in the file system.

    • Cause: When a snapshot is being created, the system identifies empty blocks to reduce the size of the snapshot. However, specific empty blocks are occupied due to various operations, such as the operations performed to format the file system, delete files, or write data. In this case, the snapshot size may be larger than the disk capacity that is displayed in the file system. This issue may occur due to one of the following reasons:

      • 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 performance 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. In this case, 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 of which data blocks in the LBA range are no longer used and can be deleted. 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 are converted into 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.

    image
    Note

    The preceding figure shows that if data is written to data blocks, the snapshot records the blocks regardless of whether the related files are deleted from the disk. In the file system, only tags are added to the headers of the files when you delete files, but the disk space used by the files is not released on the disk.

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

    When you create a snapshot or an automatic snapshot policy, you can set the Retention Period parameter to Until Deleted or Permanently (Until Deleted) or specify a retention period. After the retention period of a snapshot ends, the system automatically deletes the snapshot.

    • You can extend the retention period of a snapshot based on your business requirements. For more information, see Extend the retention period of a snapshot.

    • You can also set the Retention Period parameter in the corresponding automatic snapshot policy to Until Deleted: Created snapshots are retained based on the number of snapshots. After the maximum number is reached, the oldest snapshot is automatically deleted when a new snapshot is created. For more information, see Modify an automatic snapshot policy.

    How do I stop the billing of snapshots?

    If you no longer need snapshots, you can delete the snapshots 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 you delete existing snapshots, check whether automatic snapshot policies are being applied. If automatic snapshot policies are being applied, delete the policies to ensure that no snapshots are automatically created. 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 replaced, the instance expires, or the disk is released?

    • If you select Delete Automatic Snapshots While Releasing Disk for the disk, the automatic snapshots of the disk are released when the disk is released.

    • If you do not select Delete Automatic Snapshots While Releasing Disk for the disk, the automatic snapshots of the disk are retained for the period of time specified on the associated automatic snapshot policy.

    For more information, see the Enable or disable Delete Automatic Snapshots While Releasing Disk section of the "Modify an automatic snapshot policy" topic.

    How do I delete snapshots that were used to create images and disks?

    • You can delete snapshots that were used to create disks. After you delete a snapshot, you cannot perform operations that require the original snapshot data, such as re-initializing the system disk. For more information, see Re-initialize a system disk.

    • If you use a snapshot to create custom images, you must delete the custom images before you can delete the snapshot.

    • You can delete images that were used to create instances. After you delete an image, you cannot perform operations that require the original snapshot data, such as re-initializing the system disk. For more information, see Re-initialize a system disk.

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

    No, the automatic snapshot policy can be executed.

    Can I configure multiple automatic snapshot policies for a disk?

    No, you cannot configure multiple automatic snapshot policies for a disk. For more information, see Enable or disable an automatic snapshot policy.

    If I set the Retention Period parameter to Until Deleted when I create an automatic snapshot policy, can I delete the snapshots created based on the policy?

    Yes, you can delete snapshots created based on the policy.

    How do 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 is 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 and Roll back a disk by using a snapshot.

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

    No, you cannot use a snapshot of the original 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 Instance A after Instance A is released. If you want to use disk snapshots to restore an instance, 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 then attach the disks to Instance B. For more information, see Create a disk from a snapshot and Attach a data disk.

    Why am I unable to use snapshots of an instance to roll back the disks of the instance?

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

    What are the differences and connections between snapshots and images?

    Snapshots and images are related as follows:

    • When you create a custom image from an ECS instance, ECS creates a snapshot for the system disk and each data disk on the instance. Then, all created snapshots constitute a custom image. For more information, see Create a custom image from an instance.

    • When you delete a custom image, you can specify whether to delete the snapshots contained in the image. When you delete a snapshot, ECS checks whether the snapshot is associated with an image. If the snapshot is associated with an image, delete the image before you delete the snapshot. For more information, see Delete a custom image and Delete a snapshot.

    • You can use a system disk snapshot to create a custom image. For more information, see Create a custom image from a snapshot.

    The following table describes the differences between images and snapshots.

    Item

    Image

    Snapshot

    Nature

    An image provides the software configuration and data that are required to create an ECS instance, such as an operating system, initialization data of applications, and pre-installed software.

    A snapshot is a point-in-time backup of disk data.

    Use scenario

    • Quickly deploy environments. You can use an image to create an ECS instance with a specific environment.

    • Batch deploy environments. You can create a custom image either from an ECS instance that is deployed with specific environments or from disk snapshots. Then, you can use the custom image to batch create multiple identical ECS instances.

    • Replace operating systems. You can use an image to replace the operating system (system disk) of an ECS instance.

    • Back up disk data on a regular basis. You can use automatic snapshot policies to automatically create snapshots of disks to back up disk data on a daily, weekly, or monthly basis.

    • Back up disk data contingently. Before you perform critical operations such as updating operating systems or resizing disks, you can create snapshots to back up disk data.

    Feature

    • Images can be used to create ECS instances, but snapshots cannot.

    • An image can contain the data of only the system disk on an ECS instance or the data of both the system disk and data disks on an ECS instance.

    • An image can be used to replace the operating system (system disk) of an instance regardless of whether the image is associated with the instance.

    • Images can be copied and shared across regions or accounts. The image copies and shared images can be used to create identical ECS instances in the destination regions and accounts.

    • Snapshots can back up the data of system disks and data disks on ECS instances.

    • Snapshots can be used to restore data to disks on existing ECS instances.

    • Snapshots can be copied to back up disk data across regions.

    How do I migrate snapshots from one Alibaba Cloud account to another account?

    Snapshots cannot be migrated across Alibaba Cloud accounts. If you want to migrate a data disk snapshot from Account A to Account B, perform the following steps to create an image by using Account A based on the snapshot and then share the image with 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 with 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 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.

    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, you cannot use data disk snapshots to create custom images. You can use only system disk snapshots to create custom images.

    Can I download or export snapshots to on-premises devices?

    No, you cannot download or export snapshots to on-premises devices.

    • You can create custom images from snapshots and then export the images. Specific limits apply when you export custom images. Before you export the custom images created from snapshots, check whether the images meet the requirements that are described in the Limits section of the "Export a custom image" topic. For more information, see Create a custom image from a snapshot and Export a custom image.

    • You can also use the CloudOps Orchestration Service template named ACS-ECS-BulkyCreateAndExportImage to create custom images based on one or more instances in the corresponding region and 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 a snapshot chain?

    The message appears because your snapshot was used to create a custom image. Before you can delete the snapshot, you must delete the custom image. For more information, see Delete a custom image.