CoPA: Cold Page Awakening to Overcome Retention Failures in STT-MRAM Based I/O Buffers

Abstract

Employing a small Non-Volatile Memory (NVM) as the Persistent Journal Area (PJA) along with a DRAM-based buffer is an efficient approach to overcome DRAM vulnerability, named NVB-Buffer. Spin-Transfer Torque Magnetic Random Access Memory (STT-MRAM) is one of the most promising PJA candidates thanks to providing high endurance, non-volatility, and DRAM-like latency. Despite these advantages, STT-MRAM faces major reliability challenges, i.e. Retention Failure, Read Disturbance, and Write Failure, which have not been addressed in previously suggested NVB-Buffers. In this paper, we first demonstrate that the retention failure is the dominant source of errors in NVB-Buffers as it suffers from long and unpredictable page idle intervals (i.e., the time interval between two consecutive accesses to a PJA page). Then, we propose a novel NVB-Buffer management scheme, named, Cold Page Awakening (CoPA), which predictably reduces the idle time of PJA pages. To this aim, CoPA employs Distant Refreshing to periodically overwrite the vulnerable PJA page contents by opportunistically using their replica in a DRAM-based buffer. We compare CoPA with the state-of-the-art schemes over several well-known storage workloads based on physical journaling. Our evaluations show that CoPA significantly reduces the maximum page idle time, which leads to three orders of magnitude lower failure rate with negligible performance degradation (1.1%) and memory overhead (1.2%).