Remote cache utilization for mirrored mass storage subsystem

A digital data storage system comprising a master mass storage subsystem and a slave mass storage subsystem storing information in a mirrored storage arrangement,

• A. the slave mass storage subsystem including at least one slave data store and a slave cache memory, the slave mass storage subsystem being configured to receive update information from said master mass storage subsystem for storage in said slave data store, the slave mass storage subsystem being configured to initially cache said received update information in said slave cache memory, the slave mass storage subsystem further being configured to receive retrieval requests for information items stored in said slave cache memory and transfer the requested information item to the master mass storage subsystem;
• B. the master mass storage subsystem including at least one master data store, a master cache memory, and a host adapter, the master data store storing information to be accessed by said host adapter, the host adapter being configured to
• (i) during a storage operation, provide an updated information item to the slave mass storage subsystem during a storage operation, and maintain slave cached information identifying updated information items cached by said slave mass storage subsystem, and
• (ii) during a retrieval operation, initially determine whether an information item to be retrieved is in the master cache memory, and, if it is not, determine from the slave cached information whether the information item is in said slave cache memory in said slave mass storage subsystem and, if so, generate a retrieval request to initiate a retrieval of said information item from said slave mass storage subsystem.

A master mass storage subsystem for use in connection with a slave mass storage subsystem storing information in a mirrored storage arrangement, the slave mass storage subsystem including at least one slave data store and a slave cache memory, the slave mass storage subsystem being configured to receive update information from said master mass storage subsystem for storage in said slave data store, the slave mass storage subsystem being configured to initially cache said received update information in said slave cache memory, the slave mass storage subsystem further being configured to receive retrieval requests for information items stored in said slave cache memory and transfer the requested information item to the master mass storage subsystem;

• the master mass storage subsystem comprising:
• A. at least one master data store;
• B. a master cache memory;
• and
• C. a host adapter, the master data store storing information to be accessed by said host adapter, the host adapter being configured to
• (i) during a storage operation, provide an updated information item to the slave mass storage subsystem during a storage operation, and maintain slave cached information identifying updated information items cached by said slave mass storage subsystem, and
• (ii) during a retrieval operation, initially determine whether an information item to be retrieved is in the master cache memory, and, if it is not, determine from the slave cached information whether the information item is in said slave cache memory in said slave mass storage subsystem and, if so, generate a retrieval request to initiate a retrieval of said information item from said slave mass storage subsystem.