Data is stored in a hybrid HDD that includes a magnetic storage medium and a nonvolatile solid-state device according to multiple modes of operation: a full caching mode, a transitional caching mode, and an HDD only mode. The mode of operation may be selected based on the current condition or performance of individual storage regions in a nonvolatile solid-state device of the hybrid HDD, or on the current condition or performance of the nonvolatile solid-state device as a whole. As the nonvolatile solid-state device undergoes wear, performance of the hybrid HDD is maintained by using less reliable memory blocks in the nonvolatile solid-state device as a read cache, even when these memory blocks are considered too unreliable to store dirty data.