A hybrid storage device uses a write cache such as a hard disk drive, for example, to cache data to a solid state drive (SSD). Data is logged sequentially to the write cache and later migrated to the SSD. The SSD is a primary storage that stores data permanently. The write cache is a persistent durable cache that may store data of disk write operations temporarily in a log structured fashion. A migration policy may be used to determine how long to cache the data in the write cache before migrating the data to the SDD. The migration policy may be implemented using one or more migration triggers that cause the contents of the write cache to be flushed to the SSD. Migration triggers may include a timeout trigger, a read threshold trigger, and a migration size trigger, for example.