Introduction › CA ARCserve RHA Concepts › How Offline Synchronization Works

How Offline Synchronization Works

Offline synchronization lets you copy data to be replicated to an external device and then from the device to the Replica server. This is a method effective for transferring huge data volumes with low network bandwidth.

Consider these tips when using offline synchronization:

• You should calculate the daily change rate of the data being protected on the Master and multiply that value based on the number of days it will take for the data to reach the Replica server. For example, if your daily change rate is 2 GB and it takes 3 days before the data can be applied to the Replica, assume the spool size on the Replica to be about 6 GB. You can run scenarios in Assessment mode to derive this information.
• The spool must have enough space to hold the value you derived in your estimate. If the spool fills, scenarios must be restarted.
• You should choose Continue Offline Sync without verification unless you are certain the copy tool you are using to transfer the snapshot to the replica preserves all security attributes. ACL properties must be identical after copy operations for Offline Synchronization to complete properly. Security attribute mismatches can occur if you use normal copy tools with the verify option. Windows Explorer should not be used as it can change security attributes.

  Best Practice: Use the Continue offline sync and verify the date option or create a replication scenario to synchronize data from the VSS snapshot to external devices.

Note: You cannot use offline synchronization for scenarios with scheduled replication or scenarios in which the Master is a UNIX/Linux host.

To set up offline synchronization

1. Configure a scenario in the usual manner.
2. When you reach the final stage in the Scenario Creation Wizard, do not click Run Now. Instead, click Finish.
3. From the Manager, click Run. The Run dialog opens.
4. Select Offline Synchronization and click OK.

   After the scenario begins, the Event Console displays the path to the data so you can perform the manual copy. CA ARCserve RHA takes a VSS snapshot so you can copy data with no impact to the production data set.

   The following three points are only for Full System Scenarios, ignore if you are not using full system scenarios.

   1. The master volume generates VSS and you can find data at C:\OfflineSyncMountPoint\<scenario ID>\.

      Note: You can customize the root volume by configuring the SnapshotStorageVolume value in ws_rep.cfg.

   2. On the replica the disk volume is generated and then mounted as <install path>\Engine\vm\<scenario ID>\.
   3. To copy data from the master to the replica mount point, manually copy data from the VSS path created on the master to an external device or optical media (DVD-R, CD-R). Physically transport the external media to the Replica server.

   Manually copy the data that is stored at the master VSS path to an external device or optical media (DVD-R, CD-R). Physically transport the external media to the Replica server.

   The following example copies data to an external device.

   • Navigate to the mount point where the root directory is mounted. The default folder is C:\OfflineSyncMountPoint\<scenario-id>. Expand the directory.
   • Use a copy utility such as xcopy or fastcopy to copy data from the mounted root directories to the external storage device. For example, run the following command if the external storage device is mounted as U:

         xcopy C:\OfflineSyncMountPoint\402552372 U:\data1\ /E /C /H /R
     

   Note: Copy utilities may not copy all files due to specific limitations. For example, Windows Explorer fails to copy files that have full names (including the path) exceeding 260 bytes and Xcopy changes sparse files to non-sparse files when copied.

During transport, the production dataset caches any changes in the source data in the Replica spool.

1. Copy the data that is stored on the external media to the correct root directory on the Replica server.
2. Click Tools, Offline Sync Management. The Offline Sync Management dialog opens. Choose an option and click OK. Choose Continue Offline Sync and verify the data copies to the Replica (recommended) to confirm the data copy process or click Continue Offline Sync without verifying the data copied to Replica to skip verification. If desired, click the option to Delete VSS Snapshots created for Offline Synchronization.
3. When the validation process starts, events are shown in the Event Console. When the process is complete, the Synchronization status changes to Replication. Any changes cached in spool on the Replica during the offline sync are now committed to the Replica and deleted from the spool.