Snapshot

A snapshot is a point-in-time capture of data status in a disk. Before you perform mission-critical operations, you can take snapshots for the data volume or root volume of a VM instance so that you can immediately roll back on failure. For long-term backup, we recommend that you use disaster recovery related services.

Snapshot Management Page

In the navigation pane of the ZStack Private Cloud UI, choose Resource Pool > Snapshot. Then, the Snapshot management page is displayed, as shown in Figure 1.
Figure 1. Snapshot Management Page


The Snapshot management page has the following two tab pages:
  • VM Instance: Displays a list of VM instances that have snapshots. You can also view the VM name, VM state, snapshot count, snapshot size, and other basic information.
    • You can click the Snapshot Count drop-down arrow to sort VM instances by snapshot count.
    • You can click the Snapshot Size drop-down arrow to sort VM instances by snapshot size.
  • Volume: Displays a list of volumes that have snapshots. You can also view the volume name, volume state, volume status, snapshot count, snapshot size, and other basic information.
    • You can click the Snapshot Count drop-down arrow to sort volumes by snapshot count.
    • You can click the Snapshot Size drop-down arrow to sort volumes by snapshot size.
On the Snapshot management page, you can perform the following operations:
  • Refresh: You can refresh the snapshot list by clicking the Refresh button in the upper left corner.
  • Search: You can search for a VM instance or a volume by name by clicking the Search button next to Refresh.
  • Filter: You can flip pages or change the number of items to be displayed on each page by clicking the Filter button on the upper right corner. The number of items to be displayed on each page can be 10, 20, 50, or 100.

VM Snapshot

  • VM snapshot management:
    On the VM Instance tab page, click on the name of a VM instance. Then, the VM snapshot management page is displayed, as shown in Figure 2.
    Figure 2. VM Snapshot Management Page


    • You can create snapshots for running or stopped VM instances.
    • You cannot create batch snapshot for VM instances that have a shared volume attached.
    • In a production environment, we recommended that you limit the number of snapshots per disk within 5. Excessive snapshots might affect the I/O performance, data security, and primary storage capacity of the corresponding VM instances and volumes. For long-term backup, we recommend that you use disaster recovery related services.
    • To ensure data integrity in a production environment, we recommend that you do not take snapshots for VM instances with high I/O. When a high I/O operation is performed in a VM instance, some data in the VM memory might fail to be saved to the disk. In this case, these data will not be saved to the snapshot you created for the VM instance.
    • The snapshot of the VM instance on the Ceph primary storage does not occupy capacity. Therefore, the displayed snapshot capacity is the actual capacity of the VM root volume when the snapshot was created.
    • For Ceph primary storages, the VM snapshot capacity might fail to be obtained. Here are some statements:
      • Open source Ceph (version H) and enterprise-level Ceph (earlier than 3.2.0) cannot obtain VM snapshot capacity.
      • Due to the RBD format, enterprise-level Ceph (3.2.0 and later versions) may fail to obtain VM snapshot capacity.
  • You can perform the following operations on a VM snapshot:
    • Create: Create a snapshot for a running or stopped VM instance.
      A VM snapshot can be either a single snapshot or a batch snapshot.
      • Single snapshot: Creates snapshot only for VM root volumes.
      • Batch snapshot: Creates snapshot for both VM instances and the attached data volumes. You can recover a VM instance and its attached data volumes by recovering the batch snapshot.
        Note: Currently, if a VM instance has a shared volume attached, you cannot create snapshot for all data volumes of the VM instance at the same time.
      As shown in Figure 3.
      Figure 3. Create VM Snapshot


    • Restore: Recover data to the time of point when the snapshot was taken.
      Note:
      • For a single snapshot, you can only restore the VM root volume to the time of point when the snapshot was taken.
      • For a batch snapshot, you can restore both the root volume and data volume to the time of point when the snapshot was taken.
      • You can restore snapshots only for VM instances that are stopped. Before you restore a snapshot, stop the corresponding VM instance.
      • You can choose whether to automatically start the corresponding VM instance after restoring from a snapshot.
      • If a VM batch snapshot is displayed as not restorable, the possible reasons are as follows:
        • At least one data volume snapshot in the batch snapshot was deleted. In this case, you can only restore single snapshots.
        • At least one data volume attached by the VM instance was deleted. In this case, you can only restore single snapshots.
        • At least one data volume attached by the VM instance was detached. In this case, you can only restore single snapshots. To restore the batch snapshot, attach the detached data volumes to the VM instance again.
        • The VM instance has a new data volume attached. In this case, you can only restore single snapshots. To restore the batch snapshot, detach the new data volume from the VM instance.
    • Delete: Delete a snapshot that you no longer need. You can delete snapshots in bulk.
      Note:
      • Snapshots created on local storage, NFS, SMP, and Shared Block storages have a tree structure. Deleting the root snapshot will also delete snapshots on the branches and detach the batch snapshots on the branches. Please exercise caution.
      • Snapshots created on the Ceph shared storage are independent and do not have a tree structure. Deleting a snapshot will not affect other snapshots.
      • When you delete snapshots in a tree structure in bulk, the cloud automatically calculates and deletes the candidate snapshots and cascades the delete operation to the associated snapshots.
      • If the snapshots to be deleted contain batch snapshots, note that:
        • Deleting a batch snapshot will also delete the data volume snapshots in the batch snapshot and the snapshots on the branches. Please exercise caution.
        • Deleting single snapshots and batch snapshots in bulk will also delete the single snapshots on the branches and detach the batch snapshots on the branches.
    • Detach batch snapshot:

      Detaching batch snapshot will restore the VM snapshot to single snapshots and detach the relationship between the VM instance and related volume snapshots. The snapshots cannot be recovered in bulk after being detached. Please exercise caution.

Volume Snapshot

  • Volume snapshot management:
    On the Volume tab page, click on the name of a volume. Then, the volume snapshot management page is displayed, as shown in Figure 4.
    Figure 4. Volume Snapshot Management Page


    • In a production environment, we recommended that you limit the number of snapshots per disk within 5. Excessive snapshots might affect the I/O performance, data security, and primary storage capacity of the corresponding VM instances and volumes. For long-term backups, we recommend that you use disaster recovery related services.
    • Currently, you cannot create snapshots for shared volumes.
    • The snapshot of the volume on the Ceph primary storage does not occupy capacity. Therefore, the displayed snapshot capacity is the real capacity of the volume when the snapshot was created.
    • For Ceph primary storages, the volume snapshot capacity might fail to be obtained. Here are some statements:
      • Open source Ceph (version H) and enterprise-level Ceph (earlier than 3.2.0) cannot obtain volume snapshot capacity.
      • Due to the RBD format, enterprise-level Ceph (3.2.0 and later versions) may fail to obtain VM snapshot capacity.
  • You can perform the following operations on a volume snapshot:
    • Create: Create a snapshot for a volume.
      • You cannot create snapshots for shared volumes created on the Shared Block primary storage.
    • Restore: Restore volume data to the time of point when the snapshot was taken.
      • Before you restore a volume, you need to stop the VM instance to which the volume is attached, or detach the volume from the associated VM instance.
    • Delete: Delete a volume snapshot. You can delete volume snapshots in bulk.
      • Snapshots created on local storage, NFS, SMP, and Shared Block storages have a tree structure. Deleting the root snapshot will also delete snapshots on the branches and detach the batch snapshots on the branches. Please exercise caution.
      • Snapshots created on the Ceph shared storage are independent and do not have a tree structure. Deleting a snapshot will not affect other snapshots.
      • When you delete snapshots in a tree structure in bulk, the cloud automatically calculates and deletes the candidate snapshots and cascades the delete operation to the associated snapshots.
      • If the snapshots to be deleted contain batch snapshots, deleting the current snapshot will also delete the snapshots on the branches. After being deleted, the associated batch snapshots cannot be recovered. Please exercise caution.