Data redundancy for writes using remote storage system cache memory

A method of redundantly storing data in a computer system comprising:

• receiving a request to write data at a first storage system having at least one cache memory and mass storage;
• storing the data in the cache memory;
• forwarding redundant data to a second storage system wherein the second storage system responds by sending an acknowledgement to the first storage system;
• after receiving the acknowledgement, storing the data in the mass storage of the first storage system;
• and
• notifying the second storage system to delete the redundant data after said storing the data in the mass storage of the first storage system.

A method of redundantly storing data in a computer system comprising:

• restoring a controller in a first data storage system;
• attempting to contact a peer controller in the first data storage system;
• if said attempting is unsuccessful, determining whether the first data storage system forwarded redundant data to one or more of a plurality of remote locations;
• if the first storage system forwarded the redundant data to one or more of the plurality of remote locations, recovering the redundant data from the one or more of the plurality of remote locations;
• and
• after recovering the redundant data, forwarding data that is redundant of new data received by the first data storage system to one or more of the plurality of remote locations.

A method of redundantly storing data in a computer system comprising:

• restoring a controller in a first data storage system having mass storage and a cache memory;
• determining whether the first data storage system forwarded redundant data to one or more of a plurality of remote locations by checking the mass storage for a stored indication that the first data storage system forwarded redundant data to one or more of the plurality of remote locations;
• if the first storage system forwarded the redundant data to one or more of the plurality of remote locations, recovering the redundant data from the one or more of the plurality of remote locations;
• and
• after recovering the redundant data, forwarding data that is redundant of new data received by the first data storage system to one or more of the plurality of remote locations.