When a snapshot is created, the snapshot contains the state of the storage resource and all files and data within it at that point-in-time. A snapshot is essentially a picture of the resource at that moment in time. After creation, the space that is consumed by the snapshot is virtually zero, since pointer-based technology is used and all data within the snapshot is shared with the parent resource. The amount of data that is uniquely owned by the snapshot increases over time as overwrites to the parent resource occur as previously shown in Figure 1. In that example, after changes to the parent storage resource were made, blocks A, B, and D are only owned by the snapshot.
Users may manually create snapshots of a storage resource at any time or have them created by the system on a user-defined schedule. To have snapshots created automatically, a user must create and assign a protection policy containing a snapshot rule to a resource. Protection policies and snapshot rules are further explained in Snapshot rules. The following outlines the process to manually create snapshots on the various resources within a PowerStore system.
To create a snapshot on a resource within PowerStore Manager, go to the properties window of the resource, click the Protection tab, click the Snapshots tab, and click Create Snapshot. Figure 2 shows an example of the location of the Create Snapshot button, which is used to create a manual snapshot. This process is the same for all storage resource types, whether the resource is a volume, volume group, file system, thin clone, or virtual machine within PowerStore. In this example, the properties window for a volume is displayed.
Note: For virtual machines, the Create Snapshot operation is only supported when all storage associated with a virtual machine is provided from a PowerStore Storage Container. When the Datastore Type column on the Virtual Machines page shows vVol, snapshots are supported. When Mixed, VMFS, or NFS is displayed, creating a snapshot on the virtual machine is not supported.
When a user creates a snapshot manually, they must specify several attributes before creating the snapshot. These attributes include the Name, Description (optional), Local Retention Policy, and the Secure Snapshot setting (optional for volumes and volume groups only). The Name is the name that the snapshot is given, which is used when listing the snapshots on the resource. The Description is optional and can be used to provide more information about the snapshot, such as why it was taken or what it is used for. The Local Retention Policy determines if the snapshot should be automatically deleted in the future by the system. The Secure Snapshot setting is optional and disabled by default. When enabled, a secure snapshot cannot be manually deleted while the retention period is in effect. By default, the snapshot has a retention of seven days from the time the snapshot is created, but this can be customized by the user by providing a specific date and time for the snapshot to be deleted automatically by the system. The user can also choose No Automatic Deletion to retain the snapshot indefinitely. When No Automatic Deletion is enabled, the Secure Snapshot setting cannot be selected because secure snapshots require a retention period.
Figure 3 shows an example of the Take Snapshot window for a volume and a volume group. These windows are identical regarding the information that requested from the user. Creating a snapshot of a thin clone of a volume and volume group is similar.
When creating a snapshot of a file system, an additional option called File Snapshot Access Type is provided. The user has the option of choosing Protocol (Read-Only), which is the default selection, or Snapshot (Read-Only). The File System Access Type must be selected now, and it cannot be modified after creation.
Virtual machine snapshots can either be taken within PowerStore Manager, or within VMware vCenter. When creating a snapshot within PowerStore Manager, the user may customize the Name and provide an optional Description. Once the snapshot is created, it is displayed within the properties window of the virtual machine in PowerStore Manager and the Manage Snapshots window within vCenter.
The following figure shows an example of the Take Snapshot window.
In PowerStoreOS 3.0 and later, users can see how many snapshots currently exist on a resource by viewing the Snapshots column. This column has been added to the volumes, volume groups, file systems, or virtual machine pages so that users can see how many snapshots exist on each resource. This column is hidden by default but can be added to the view using the Show/Hide Table Columns option.