1. A method comprising: receiving a write request that includes a write data and an address of a target block in tertiary storage, wherein the tertiary storage is tape storage; detecting a write-miss at a cache in response to the write request, the cache located in persistent storage; and in response to detecting the write-miss: writing the write data and associated metadata to a fast write storage location in a fast write data storage and not to the cache, and marking the write request as complete, wherein the fast write data storage is separate from the cache; retrieving the target block from the address in the tertiary storage; storing the target block in the cache; and merging contents of the fast write storage location with the contents of the target block in the cache.