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Fast failback versus difference-based synchronization

In the case of fast failback, the data blocks that changed while the original Primary was unavailable are tracked using the DCM for each volume. Difference-based synchronization computes MD5 checksums for a fixed size data block on the Primary and Secondary data volumes, compares it, and then determines whether this data block needs to be transferred from the Primary data volume to the Secondary data volume. The fast failback feature is recommended over the difference-based synchronization for the following reasons:

The following sections describe each of the above methods for failing back to the original Primary.