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Migration process and phases

The data and configuration migration process using the 7-Mode Transition Tool consists of the following phases: preparation, baseline data copy, precutover, and storage cutover. You should understand the phases to manage the transition effectively.

The following image shows the different phases in the migration process:



Preparation

In this phase, prechecks are run to verify feature functionality. The process checks the 7-Mode storage systems to verify that the volumes and configuration are ready to be migrated to clustered Data ONTAP. It checks that the cluster is configured properly and is able to support the transition. Any errors must be resolved before continuing with the transition. Although the tool allows you to continue without resolving warnings, it is a best practice to address any warnings before continuing with the migration. You can run the prechecks multiple times to verify that all the errors have been resolved.

Although the precheck step and assessment steps performed during the assessment appear to be similar, there are differences. The precheck step is a more detailed test that is focused on the specific storage systems that have been identified as the migration source (7-Mode) and destination (clustered Data ONTAP) systems. The assessment step only evaluates the migration source systems, checking feature and functionality differences with clustered Data ONTAP.

Baseline data copy

New volumes are created on the SVM, a SnapMirror relationship is established between the 7-Mode and clustered Data ONTAP volumes, and a baseline transfer is performed. After the baseline is complete, incremental transfers are automatically run according to a user-defined schedule. Clients and servers accessing the source storage remain online while this step is completed.

Copying data requires CPU, memory, and storage access, which results in additional resources being used on the source storage system. It is a best practice to schedule data copy activity to occur during off-peak times (preferably, CPU usage should be around 50%).

Precutover

This phase includes SnapMirror incremental transfers; configuration information is applied to the clustered Data ONTAP system, SVM, and volumes. Optionally, you can also test the clustered Data ONTAP volumes that are being transitioned before storage cutover.

Although a majority of the configuration is applied, some actions are deferred to storage cutover: for example, applying quotas.

Tip: Although incremental updates are not required, it is a best practice to perform an incremental transfer as close to the storage cutover as possible so as to minimize the time that clients are disconnected.

Storage cutover

At a high level, during storage cutover, clients are disconnected, a final data transfer is performed, the SnapMirror relationship is broken, and clients are manually reconnected.

Disconnecting clients or servers from the source storage volume prevents additional writes from being performed while the final copy is being executed. Before disconnecting clients, it is a best practice to perform an incremental update to minimize the downtime.

Storage access must be disconnected only for the volumes that are being migrated. Access to storage can be discontinued from the storage side or the client side. The best practice is to discontinue connectivity from the storage side. For example, if a CIFS client is accessing a volume named "user01" on a 7-Mode storage system, you can use the cifs terminate -v user01 command to disable access to all the CIFS shares on the volume (discontinuing client access from the storage side). The IP addresses, mount points, or even share names might change as a result of the migration, and therefore client access might be discontinued from the client side as well. As long as clients cannot write any new data to the storage container that is being migrated, you can use either or both of these methods for discontinuing access.

After clients are disconnected, the 7-Mode Transition Tool executes a final copy so that both the source and destination datasets are at parity. The 7-Mode Transition Tool configures the data LIFs on the SVM. Some configuration changes, such as applying SAN configurations and quotas, that were not transitioned during precutover are also applied to the SVM at this time.

After storage cutover finishes, you can manually reconnect the clients and validate data access. Validating data access involves verifying that clients are accessing the clustered Data ONTAP system properly and that all permissions are working as expected.