Provisioning memory in a memory system for mirroring includes: gathering, by a memory controller, margin data for memory in the memory system, the margin data representing susceptibility for error; identifying, by the memory controller in dependence upon provisioning criteria and the margin data, mirroring candidates within the memory system; and mirroring, by the memory controller, memory of the memory system utilizing the mirroring candidates as a mirrored backup of other memory in the memory system.