Knowledge Base Article #:
CA ARCserve RHA R16
June 21, 2012
The following explains what Offline Synchronization is and how it is implemented.
Offline synchronization (Available only from the Run dialog)
In offline synchronization, data is copied from the Master server to an external device and from the external device to the Replica server. This method is best suited for transferring huge volumes of data without any adverse impact from low network bandwidth.
This option is available only when running a scenario and does not apply to Full System HA scenarios, scenarios with scheduled replication, or scenarios in which the Master is a UNIX/Linux host.
The following example uses a SQL DR Scenario to demonstrate how offline synchronization is achieved (Any screens that are not pertinent to offline synchronization during the scenario creation process have been omitted).
- Server Type (Microsoft SQL Server) and Product Type (DR) are selected.
- Scenario is named ("Offline Sync") and Master and Replica nodes are defined.
- Replica Root directory defined in the scenario matches that of the master.
- When Scenario Run screen is reached, select the "Finish" button. Selecting "Run Now" will not give the option to enable Offline Synchronization.
- Start the scenario by selecting the green "Run" button.
- The Run dialogue screen will appear. Select "Offline Synchronization".
- Once the scenario begins an event will display showing the path to the data that is ready for manual copy.
- A VSS snapshot of the data is taken which allows the data to be copied without impacting the production data set. Since this data is static there are no processes locking the files which may impact the ability to copy them. Data can be backed up to tape, removable hard drive or optical media (DVD-R, CD-R) and transported to the replica server via a method which is not reliant on the slow network link.
- While the master's data is being shipped to the replica, CA ARCserve RHA will send any changes introduced on the master server within the selected root directories to the replica. The replica server will cache these changes in spool.
- Once the data arrives at the replica server and is manually copied into the correct root directory the data can be validated by selecting Tools > Offline Sync Management.
- The Offline Sync Management window appears and gives the option to Continue Offline Sync and verify the data (recommended) or to skip this validation process. There is also a check box to delete the VSS Snapshots which were created on the master server.
- Once the validation process is starting a real time account of the events will be displayed in the RHA Manager Event Console. Once completed the Offline Synchronization status changes to Replication.
- Replication occurs once the data on the replica is synchronized with the data on the master server. Any of the changes sent to the replica which were cached in spool on the replica during offline sync are committed to the replica and flushed from spool.
Planning considerations when using Offline Synchronization:
- For Offline Synchronization to be successful it is important to calculate the daily change rate of the data which is being protected on the master, and multiply that value based on how many days it will take for the data to reach the replica server and be applied.
If daily change rate is 2GB and it will take 3 days before the data can be applied to the replica the spool buildup on the replica will be approximately 6GB.
If you are unsure of your daily change rate you can run the scenario in Assessment mode to derive this information. Assessment mode will monitor changed data on the master but no physical data is sent to the replica. For more information on assessment mode refer to CA ARCserve RHA Admin guide section entitled "Running a Scenario in Assessment Mode"
- The spool drive defined on the replica will need to have enough space to hold the value derived in Step 1. If spool fills on the replica server the scenario will stop and process will need to be stared over.