Introduction › CA ARCserve RHA Concepts › How Synchronization Works › Synchronization Methods

Synchronization Methods

To properly synchronize the Master and the Replica, it is first necessary to perform a comparison of their two file structures. This comparison determines what content (files and folders) on the Master is missing or different from that on the Replica. There are two ways to start Synchronization:

• Click the Synchronize button on the Manager toolbar
• Click the Run button on the Manager toolbar

Select a synchronization mode, each with a different comparison algorithm and method of operation:

• File synchronization

  In file synchronization, the Replica server sends its snapshot to the Master server, which uses it to drive the information and content for the data comparison. After the comparison is performed, the Engine on the Master server sends a sequence of commands to the Replica. These commands:

  • delete files that exist only on the target
  • list the entire file contents of files that either exist only on the Master, or that exist on the Replica but differ from the version on the Master

  This method is best suited for File Servers or application servers with a large number of relatively small files.

  Note: When performing File Synchronization, CA ARCserve RHA does not update the data transferred percentage until the file transfer is completed.

• Block synchronization

  In block synchronization, the Engine performs a block-by-block comparison of the Master and Replica files, and copies over only those blocks that are different. When differences exist between files, instead of requiring the transfer of the entire file, block synchronization transfers changes only.

  This method is best suited for database applications, such as Microsoft Exchange Server, Oracle, and SQL Server, or application servers with very large files.

• 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 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. For more information, see Running the Replication Process.

The comparison may be configured to consider only file size and modification time to determine whether two files differ, or it can perform a check of the actual contents of the data. The former approach, which is not valid in the case of database applications, can be a legitimate way to significantly speed up the comparison process on a File Server scenario.

You may also Filter or Skip synchronization.