1. A method of failure mapping, comprising: distributing user data throughout a plurality of storage nodes through erasure coding, wherein each of the plurality of storage nodes has a non-volatile solid-state storage with non-volatile memory; determining that the non-volatile memory has a defect; generating a mask that indicates the defect, the generating based on error correction of reads of the non-volatile solid-state storage, wherein the mask is one of a plurality of masks in a mask hierarchy in the storage cluster, wherein the mask hierarchy includes masks of differing physical levels of the non-volatile memory, and wherein the generating supports combining the masks of differing physical levels to generate one or more page specific masks; and reading from the non-volatile memory with application of the mask, wherein the reading and the application of the mask are performed by the non-volatile solid-state storage.