Several operations are available to manipulate replication sessions as needed. Not all operations are always available, because some depend on the resource type and on the session being in a particular state. Also, certain operations perform differently depending on which system they are issued on—the source or destination. Only one replication operation can be issued and run at a particular time. Replication operations are available when browsing the storage resource details and then selecting the PROTECTION > REPLICATION tab or by browsing to the Protection > Replication section.
The PAUSE and RESUME functions can stop and start replication between the resources for a particular replication session (see Figure 34 and Figure 35). In PowerStore Manager, the pause operation is issued from the source or destination system. If the session is paused while an initial sync or an incremental synchronization is in progress, all incremental changes on the destination are kept. All I/O is kept in a snapshot diff when the replication session is paused. When the session is resumed, replication resumes and the synchronizations to the destination storage resource continue from where they were paused. When a replication session is paused, it also pauses the scheduled RPO synchronizations. The resume operation can be issued on the source or destination system and does not change the replication direction.
With asynchronous replication, updates to a destination storage resource occur at a set interval that is based on the defined RPO. When replication is established and an update is not occurring, a SYNCHRONIZE NOW operation can be issued to synchronize the latest changes to the destination resource (see Figure 36). After the sync operation is selected, all data that has changed since the last update is copied to the destination storage resource.
A PLANNED FAILOVER operation allows for replicating the latest acknowledged host data on source volume while also performing a controlled failover (Figure 37). When initiating the operation, the following dialog also allows optionally selecting Reprotect after failover. When a planned failover starts, the replication session fails over after completing a synchronization between the volumes. The synchronization before failover ensures that all data is replicated since the last RPO triggered or manual synchronization. The planned failover option is available on the source storage resource when the replication session is “Operating Normally” or a synchronization is in progress. It causes a short period of data unavailability during the failover operation. Before the Planned Failover operation is issued, it is suggested to issue a manual sync first. This action reduces the amount of data to copy during the planned failover. Quiesce I/O to the source volume before performing a planned failover. After the planned failover is completed, the destination storage resource is available for production I/O, and the original source no longer allows read/write I/O. If host access is configured on the destination resource, hosts can access the data. If reprotect after failover is not selected when initiating the failover, replication does not resume in either direction.
The unplanned failover option is only available on the destination of the replication session. This failover type fails over to the latest available common base image that exists at the target without any synchronization occurring beforehand. An unplanned failover assumes that a disaster has occurred on the production system, and the destination image is made read/write. When FAILOVER is selected on a destination resource of a replication session (Figure 38), read/write access is removed from the original source if the source is available to receive management commands. The replication session also pauses and does not automatically switch the direction for replication. The replication session is left in this state until the user issues another replication operation. If I/O occurs to the original destination resource while in this state, the data must be replicated back to the original source when the source becomes available. For file resources, FAILOVER is not supported on the destination resource if the source system and production NAS server are still online. If the source is still functioning, issue a PLANNED FAILOVER from the source.
PowerStore allows initiating an unplanned failover operation during a disaster scenario or even when the replication is in a Paused, Failing Over, or Failed Over state. Any changes made on the source system while the session is in these states might not be replicated to the destination. Since no final synchronization is performed, an unplanned failover can result in data inconsistency or data loss. It should be only initiated when the source system is not available anymore. Use a planned failover whenever possible (see Planned failover).
After the Planned Failover or Failover option is used, the REPROTECT option (Figure 39) becomes available on the new source system. It is also triggered after a planned failover with the reprotect operation is initiated. The reprotect operation starts the replication session and synchronization to the original source system. Because there might not be synchronized changes after an unplanned failover on the destination, taking a snapshot on the remote system before the reprotect operation is initiated is recommended.
A replication session can be deleted on the source system by detaching the protection policy from the replicated storage resources or by removing the replication rule from a protection policy. Figure 40 shows the option to Unassign Protection Policy. When there are no configuration issues and an unassign operation is issued on the source system, the replication session is deleted from the source and destination systems. The destination storage resource is not automatically deleted when the replication session is deleted.
This function allows testing the DR functionality and is only supported on volumes, volume groups, and thin clones. Dell PowerStore provides the Failover Test to enable R/W access to the DR site while production is still ongoing on the primary system (Figure 41).
It is possible to start a failover test only on the replication destination (Figure 42) for each storage resource participating in a replication session.
After START FAILOVER TEST is selected to initiate a failover test, you must select a snapshot, which will be used as the source of data for the DR test. You can select either the last successful synchronized RPO snapshot or any other existing manual or scheduled snapshot on the destination system for DR test (Figure 43).
As soon as the failover test starts, the storage resource changes to Read/Write for the mapped host. While failover test is activated, test data writes are stored in the mapped volume and replication continues in background using a read/write snapshot. All updates from the replication source are baselined and kept in a replication snapshot. PowerStore has no limit on the duration of the DR Test.
The following section describes the options to stop a DR failover test:
When stopping a failover test, the access changes back to read-only for the DR Host. The PowerStore Manager provides an optional step to keep test data in a snapshot for later use before the DR host volume is updated with the last successful synchronized snapshot data (Figure 44). A snapshot of test data might be useful when test data should be used or analyzed later. Otherwise, the DR host volume is immediately updated with the last successful synchronized snapshot data.
If there is a real DR issue while the failover test is running, there is no further update of the destination volume from the source, and the test data is used for DR production. For this scenario, the operator has to confirm the following dialog (Figure 45).
PowerStore supports cloning the destination NAS server. This feature is designed to enable DR testing without any impact to the ongoing replication session or the production NAS server. It allows customers to confirm that an application can be brought online and write to a share hosted on the destination system.
On the destination system, the user selects the destination NAS server and selects MORE ACTIONS > Clone. A new name is provided, and then the user selects the file systems that the user wants to create with the cloned NAS server. Any shares that exist on the selected file systems will also be cloned. When all information is provided, click CREATE.
The cloned NAS server is created without a file interface to ensure that there is no conflict with the production NAS server. In order to access the cloned file systems, a new file interface must be added to the cloned NAS server on the NETWORK page of the NAS server. The cloned NAS server is not domain joined automatically. If the cloned NAS server must be domain joined, a unique name needs to be specified before the join operation. After it is cloned, the new NAS server is a stand-alone resource and functions independently from the parent DR NAS server. The NAS server clone operation is not limited to DR testing, and source or even nonreplicated NAS servers support cloning. For more details, see the .
When replicating a NAS server, the destination NAS server may require different configuration settings than the source NAS server. PowerStore supports the ability to modify the destination NAS server and make these configuration changes before failing over. Therefore, if a failover needs to occur, the destination NAS server will be fully functional when it is promoted to a production instance. The following NAS server configuration options are available for modification on the destination:
To modify the destination NAS server, go to the NAS Servers page on the destination PowerStore system and click into the NAS server. Modify the settings directly on this NAS server. For example, to support a different IP address on the destination NAS server, select the interface on the NETWORK page and click MODIFY. Then select Override and enter the new destination IP address.