Storage processor hardware upgrade in a storage system

A method for upgrading storage processors in a storage system comprising a storage processor enclosure comprising a first storage processor comprising a first cache, and a second storage processor comprising a second cache, the second storage processor connected to the first storage processor by a first cache mirroring connection;

• and a disk enclosure comprising a plurality of disk units forming a plurality of logical units, wherein the disk enclosure is connected to the first storage processor and the second storage processor, the method comprising:
• servicing, by the first storage processor and the second storage processor, IO requests for the plurality of logical units;
• mirroring, by the first storage processor and the second storage processor, the first cache and the second cache via the first cache mirroring connection;
• replacing, in the storage processor enclosure, the first storage processor with a third storage processor comprising a third cache while the second storage processor services the IO requests for the plurality of logical units;
• servicing, by the second storage processor and the third storage processor, IO requests for the plurality of logical units;
• mirroring, by the second storage processor and the third storage processor, the second cache and the third cache via the first cache mirroring connection;
• replacing, in the storage processor enclosure, the second storage processor with a fourth storage processor comprising a fourth cache while the third storage processor services the IO requests for the plurality of logical units;
• servicing, by the third storage processor and the fourth storage processor, IO requests for the plurality of logical units;
• and
• mirroring, by the third storage processor and the fourth storage processor, the third cache and the fourth cache via the first cache mirroring connection.

A storage system comprising:

• a storage processor enclosure comprising:
• a first storage processor comprising a first cache, and
• a second storage processor comprising a second cache, the second storage processor connected to the first storage processor by a first cache mirroring connection;
• and
• a disk enclosure comprising a plurality of disk units forming a plurality of logical units, wherein the disk enclosure is connected to the first storage processor and the second storage processor;
• wherein the first storage processor and the second storage processor are configured to service IO requests for the plurality of logical units and mirror the first cache and the second cache via the first cache mirroring connection;
• wherein the second storage processor is configured to service the IO requests for the plurality of logical units while the first storage processor is replaced with a third storage processor comprising a third cache;
• wherein the second storage processor and the third storage processor are configured to service IO requests for the plurality of logical units and mirror the second cache and the third cache via the first cache mirroring connection;
• wherein the third storage processor is configured to service the IO requests for the plurality of logical units while the second storage processor is replaced with a fourth storage processor comprising a fourth cache;
• and
• wherein the third storage processor and the fourth storage processor are configured to service IO requests for the plurality of logical units and mirror the third cache and the fourth cache via the first cache mirroring connection.