Gold Copy represents a virtual point-in-time copy of the secondary LUN before the secondary LUN is updated with the changes from the primary LUN. Since it is a pointer-based virtual copy it only consumes space in the reserved LUN pool based on the amount of changes on the secondary LUN. During the secondary LUN update, the Gold Copy tracks all of the updates. When a region on the secondary is updated, the original region is copied to the reserved LUN pool to preserve a consistent point-in-time view of the secondary LUN at the time of start of update. This is a key feature that always ensures a consistent view of the secondary LUN. If the update from primary to secondary is interrupted due to a link failure or due to failure at the primary site (during the update), the Gold Copy is used by MirrorView/A software to rollback the partial update on the secondary LUN and return it to its previous consistent state.
Delta Set : MirrorView uses asynchronous writes, which means that I/O is not sent to the remote site at the same time as the host I/O. It is a periodic replication of a set of LUNs to a remote storage system. The Delta Set is created and changes are tracked during a MirrorView/A replication cycle. MirrorView/A replicates only
the last changed blocks during replication cycle and results in lower bandwidth requirement than synchronous or traditional native ordered write techniques. The Delta Set is, in reality, a local snap taken at the source side at the time of replication.