In addition to being created manually, snapshots can be created automatically by the system at a specific time of day, or at a defined interval. Within PowerStore, protection policies are used to achieve automatic data protection on resources. A protection policy is a group of user-defined rules that are used to establish local or remote data protection on an assigned storage resource. In PowerStore, administrators can assign a protection policy to the resource which defines the level of protection. Protection policies are also created on the cluster, and not an individual appliance. This means that any resource on any appliance in a multi-appliance cluster can leverage a protection policy once it is created. Only one protection policy can be assigned to a resource at a time.
To achieve automatic snapshot creation and deletion on a resource, this first step is to create a snapshot rule. To create a snapshot rule in PowerStore Manager, go to Protection > Protection Policies > Snapshot Rules. An example is shown in Figure 21. On this page the current snapshot rules are displayed, along with information about each rule. Starting in PowerStoreOS 3.5, the Secure Snapshot Enabled column can be added to the view as shown in the following figure. This column shows which snapshots have the Secure Snapshot setting enabled. To create a rule, click Create.
The Create Snapshot Rule window is then displayed. This allows the user to customize when snapshots are automatically created within the system. An example of this window is shown in Figure 22. The first entry in the snapshot rule is the Rule Name. Providing a unique name allows the user to quickly identify what protection the rule is set to achieve, such as the names used in Figure 21. In the example, names such as Daily Snapshot-7days and Hourly Snapshot-7days are used.
Next is Days, which defines which days of the week to run the snapshot rule and create a snapshot. By default, all days of the week are selected. The user can clear the box for days where a snapshot is not needed. This action may be done to limit the rule to one day per week, or on certain days such as workdays.
Next is the Frequency/Start Time, which tells the system how often to create snapshots automatically within the system. The user can either choose a fixed interval to create snapshots or specify a specific time. By default, Every 6 hours is selected. The drop-down box next to Every allows the user to choose other intervals, ranging from 5 minutes to 24 hours. The Time of day option allows the user to choose a particular time of day to create snapshots.
The next option is Retention, which tells the system when to automatically delete the snapshot. Snapshots that are created by a snapshot rule always have a retention value set, but the Retain Until value can be changed on an individual snapshot by the user at any time. The retention value is based on a Keep For value, which indicates to the system the number of Hours or Days to retain the snapshot. When the snapshot is created, the Retain Until value for the snapshot is set to match the retention value of the snapshot rule.
The available choices for the Keep For value directly depends on the Frequency/Start Time. The more often the snapshots are set to be created, the shorter the available retention period. This behavior ensures that the snapshot rule does not exceed the maximum number of snapshots that are allowed for a resource. If the resource has a protection policy that is assigned to it that contains several snapshot rules, then the oldest snapshot set with an expiration date is deleted automatically to allow for the new snapshot to be created. When configuring protection policies, ensure that the selected rules do not result in exceeding the maximum number of snapshots that are supported on the resources. System limits can be found in the Dell PowerStore Support Matrix.
The Secure Snapshot checkbox is available to enable secure snapshot creation by a snapshot rule. When the Secure Snapshot box is checked, all snapshots created using the rule will have the Secure Snapshot setting enabled. Any snapshot with the Secure Snapshot setting enabled cannot be deleted by the user and will automatically expire when the retention period is met. If the Secure Snapshot setting is enabled on an existing snapshot rule, any snapshots created previously will remain unchanged and have the Secure Snapshot setting disabled. Users can manually enable the Secure Snapshot setting on each snapshot created previously if necessary. When the Secure Snapshot setting is disabled on a snapshot rule, any future snapshots created by the rule will have the Secure Snapshot setting disabled, and any previously created snapshots will remain unchanged. A snapshot rule with the Secure Snapshot option enabled can be applied to a File resource, however the File snapshots will ignore the secure snapshot setting because secure snapshots are only supported on volumes and volume groups.
The last option in the Create Snapshot Rule window is the File Snapshot Access Type setting. This setting, which is displayed in Figure 23, is only enforced for file-based resources. By default, a Protocol (Read-Only) snapshot is created on file systems and file system thin clones by the snapshot rule. The user can optionally create Snapshot (Read-Only) snapshots by the rule.
In PowerStore Manager, the times that are displayed are adjusted to the local time zone. When the snapshot rule is created and the Time of day option is used, systems running PowerStoreOS 1.0 takes the value and stores it in UTC format. UTC does not adjust for seasonal time changes. If you live in an area where seasonal time changes occur, the snapshot creation time does not adjust to account for this change. It is possible for snapshots that are automatically taken to be taken one hour prior or one hour past the target time due to seasonal time changes, depending on when the rule was created. To correct this issue, edit the snapshot rule and change the time to overwrite the time stored within the system.
Available in PowerStoreOS 2.0 and later, snapshot rules configured with the Time of day option will be associated with a time zone. This time zone association ensures that snapshots will be taken at the correct time if the specified time zone practices Daylight Saving Time (DST). DST is the process of advancing clocks during warmer months so that darkness falls later each day according to the clock. If the specified time zone practices DST, the rule will automatically adjust when the time is advanced or set back based on this practice. The default time zone will reflect the local time zone of the client; however, administrators can modify the time zone if they so choose. Prior to this feature, the Time of day setting selected will be converted to UTC on the system. This can result in a timing shift of snapshots relative to the client time, depending on when the rule was created and if the time zone is entering or leaving DST.
After a snapshot rule is created, it must be added to a protection policy and assigned to a resource before snapshots are automatically taken. On the Protection Policies page, click Create to create a protection policy, or modify an existing policy to add the rule. Click Create, and the window in Figure 24 is displayed. The user can specify the name of the protection policy and assign snapshot rules, a replication rule, and a remote backup rule to it. A protection policy can contain up to four snapshot rules, one replication rule, and one remote backup rule. Users can also create a snapshot, replication, or remote backup rule when creating a protection policy if needed.
When the protection policy is created, it is displayed on the Protection Policies page. On this page, you can see the number of snapshot rules that are contained within each protection policy, the replication rule that is assigned to the policy (if one exists), and how many resources have the policy assigned to it. In this example, multiple protection policies have been created based on the needs of the business. The Gold Policy has one more snapshot policy that is assigned to it compared to the Silver Policy. The names that are displayed here are only used as an example.
To quickly view which snapshot rules are assigned to a protection policy, hover over the value within the Snapshot Rules column. This action gives a quick glance as to which snapshot rules are contained within the protection policy.
Assigning a protection policy to a resource can be completed multiple ways. This task can be completed from the resource list page for volumes, volume groups, or file systems, and from the Snapshots tab within the Protection tab within the properties of a resource. Figure 27 shows an example of the File Systems page and the Protect drop-down menu. From here, a user can either assign or unassign protection policies from multiple resources at a time. The volumes and volume groups pages have similar methods. In each of these windows, the Protection Policy column is available and lists the protection policy that is assigned to the resource.
Note: In PowerStoreOS 3.0 and later, protection policies can no longer be assigned to Virtual Machines. For automatic snapshot creation, VMware vSphere storage policies should be used. Any existing protection policies added to virtual machines on previous codes will remain and can be unassigned at any time. For more information about VMware and data protection, see the white paper on the .
When viewing the Snapshots tab under the Protection tab within the properties of a resource, the option to assign a policy is available. For resources that do not have a policy applied, the message in Figure 28 is displayed. The user can optionally click the Assign Policy button to add a protection policy to the resource.
If a policy is assigned, the name of the policy is displayed on the Protection tab itself, and in the Snapshots tab within the same window. An example is shown in Figure 29. From the Snapshots tab, the protection policy that is assigned to the resource can be updated by clicking the Change button.
To quickly view the rules contained within the protection policy, hover over the protection policy name within the Protection tab or the Snapshot tab. This action provides an easy way to view the current rules rather than browsing back to the Snapshot Rules page.
Protection policies and snapshot rules can be edited at any time. Users can quickly add and remove rules from protection policies as needed. If a snapshot rule is edited, the changes are automatically propagated to any protection policies and resources that are currently using the rule. As an example, the user may choose to change the retention for the snapshots created by a particular snapshot rule. If this action is done, any new snapshots are created with the new retention policy. Also, any snapshots that were created using the rule also have their retention updated to reflect the new retention value.
If a snapshot rule is no longer needed, it can only be deleted if it is not in use by any protection policies. Figure 30 shows the Delete Snapshot Rule window. When deleting a snapshot rule, the user also can optionally delete any snapshots that are created by the rule. This action allows the user to quickly delete snapshots that are no longer needed. Any secure snapshots created by the rule will not be deleted if the box is checked. Those snapshots will be automatically deleted when they expire.