RETROFIT: Fault-Aware Wear Leveling

Phase-change memory (PCM) and resistive memory (RRAM) are promising alternatives to traditional memory technologies. However, both PCM and RRAM suffer from limited write endurance and due to process variation from scaling, increasing number of early cell failures continue to put pressure on wear-leveling and fault tolerance techniques. In this paper, we propose RETROFIT, which leverages the spare “gap” row used as temporary storage in wear leveling to also be used strategically to guard against early cell wear out. RETROFIT is compatible with error correction schemes targeted at mitigating stuck-at faults and provides benefits when single or multiple spare rows are available. RETROFIT enhances lifetime by as much as 107 percent over traditional gap-based wear leveling and 8 percent over perfectly uniform wear leveling with a similar overhead. Furthermore, RETROFIT scales better than wear-leveling combined with error correction as process variation increases.