1. A method, comprising: partitioning a plurality of processing nodes in a storage system into a plurality of logical processing units, wherein the plurality of logical processing units can respond to I/O requests from a host coupled to the storage system; grouping at least two logical processing units, wherein data in a first storage coupled to a first logical processing unit of the least two logical processing units is mirrored by data in a second storage coupled to the second logical processing unit of the at least two logical processing units; and in response to a failure of the first logical processing unit, responding to an I/O request from the host via the second logical processing unit.