Data storage reliability is maintained in a write-back distributed data storage system including multiple nodes. Each node comprises a processor and an array of failure independent data storage devices. Information is stored as a set of stripes, each stripe including a collection of at least a data strip and associated parity strips, the stripes distributed across a primary data node and multiple corresponding parity nodes. A read-other parity update protocol maintains parity coherency. The primary data node for each data strip drives parity coherency with the corresponding parity nodes, independently of other data nodes, in keeping relevant parity strips for the primary data node coherent. A parity value is determined based on data other than a difference between new data and existing data. A new parity value is based on new data and dependent data, wherein with respect to one data value, dependent data comprises other data encoded in a corresponding parity value.