1. A method of performing garbage collection in a hybrid memory system that includes a primary memory and a secondary memory, the method comprising: performing a read operation comprising reading data from a first cluster of a plurality of clusters; responsive to a determination that the read operation failed, unmapping the first cluster without writing the data to a second cluster and continuing to use the first cluster for subsequent data storage; and responsive to a determination that the read operation did not fail, writing the data to the second cluster.