Contemporary storage systems often maintain at least three replicas of all data, reducing the risk of permanent data loss due to simultaneous disk failures. The cost of the additional copies is a reduction in usable storage space, with increased network traffic and higher power consumption. The presented technology employs an inexpensive add-on device attached to each disk, enabling storage systems to withstand simultaneous failures while requiring only two data replicas and minimizing cost, network, and power overheads.