Performing Data Verification

VVR provides two methods to validate the data at the Secondary site; online data verification and offline data verification. These methods are used to verify that the data on the Secondary data volumes is identical to the Primary data volumes.

• Online data verification allows you to validate the date even when the replication is in progress. In this method instead of the actual volumes the point-in-time snapshots are compared. This method is referred to as online data verification.
• Offline data verification can be performed only when the replication is not active.

Verifying RVG Offline

Offline data verification can be performed only when the replication is not active and can be used in two situations:

• If you have already created the Primary and Secondary volumes and replication is in progress, you can pause replication when the Secondary is up-to-date. Then perform data verification between the corresponding Primary and Secondary volumes to make sure that the data volumes on the Primary and Secondary are the same. This command performs a comparison of the checksums on the corresponding Primary and Secondary volumes.
• Before adding new volumes to the RDS, you can validate the data on the new volume. If you find that the Primary data and Secondary data do not match, then you can use some manual means such as backup and restore or some other method to make the data on the new secondary volume the same as the Primary and then add it to the RDS.

VVR enables you to verify whether the data on the Secondary is identical to the data on the Primary data volumes when the application is inactive. The Verify RVG Offline task verifies and reports any differences between the data volumes associated with the Secondary RVG and the corresponding Primary RVG. The Verify RVG Offline task only reports whether the Primary and Secondary volumes are identical or not. It does not make them identical.

Prerequisite:

  Make sure that any applications writing to the Primary data volumes are stopped before starting the verification of the RVG.

  To verify RVG offline

1. Pause replication to the Secondary that is to be verified.
2. Select the Secondary RVG to be verified.
3. From the Secondary RVG view, select Tools > Verify RVG Offline.
4. Complete the Verify RVG Offline dialog box as follows:

   Secondary Host	Select the Secondary host.
   Option: Display output in reverse order.	Select the checkbox only if you want to view the output of Verify RVG in reverse order.

5. Click OK. A message displays the status of the operation.
6. Click Close.

Verifying RVG Online

The space-optimized snapshots that are created using the Snapshot wizard can be used to verify whether the data on the Primary and Secondary RVG volumes is the same. The major advantage of this feature over the Verify RVG Offline task is that you do not need to stop the replication. The verification can be done even while the replication is in progress because the point-in-time snapshots, and not the volumes, are compared. This feature is useful if you want to check the integrity of the data volumes on the Secondary when replication is in progress.

The Verify RVG Online task creates the space-optimized snapshots on the Primary and the Secondary before it proceeds with performing online data verification. The Verify RVG Online task also ensures that the snapshots are taken only after the replication has been paused using the vxibc freeze command.

As a result there may be a momentary pause in the replication. It is necessary to freeze the writes so that the snapshots can be taken at an identical point in replication time, on each of the required hosts.

The Verify RVG Online task then verifies the data between the remote and local hosts by comparing the space-optimized snapshots.

Prerequisite:

  Volumes must be prepared for instant snapshots.

To perform online data verification:

1. Select the Secondary RVG for the RDS that you want to verify.
2. From the Secondary RVG view, select Tools > Verify RVG Online.
3. Complete the option page as follows:

   You must specify either a cache size or a cache name.

   Cache Size	Select Cache Size and specify a default size for the cache object with respect to the source volume. The default is Megabytes. Select another unit from the drop-down menu, if necessary.
   Cache Name	Select Cache Name and specify a name for the pre-created cache object on which the snapshots for the volumes in the specified RVG will be created.

4. Click Next. Specify additional options as follows:

   Other options: Destroy the cache object and the snapshot volumes after the data verification has completed.	Check this option to destroy the snapshot volume and the cache object after the data verification has proceeded successfully. This is the default.
   Keep the cache object but destroy the snapshot volumes.	Check this option to preserve the cache object to be reused when creating future snapshots.
   Keep the cache object and the snapshot volumes.	Check this option to preserve the snapshot volumes. The cache object is also preserved along with the snapshot since the snapshot cannot exist without the cache object.

5. Click Finish.
6. The Summary shows. Select the checkbox for the option if you want to display output in reverse order. Click OK.
7. The Status shows. Click Close.