Methods and structures for limiting the write portion of a local cache memory in one or more disk drives of a storage system such that a storage controller coupled to each may mirror the content and structure of the write portion of each disk drive. The size of the write portion of the local cache memory in a disk drive controller may be controlled by the storage controller or other host device. The size of the write portion may be controlled by switch settings to select among a plurality of predefined sizes or may be programmed by the storage controller or other host device. Programming such a size value may be by setting parameter values in a configuration page of a SCSI disk drive's local memory or may be by a vendor unique command sent by a host device to the disk drive.