  This work investigates a new erase scheme in NAND flash memory to improve the
lifetime and performance of modern solid-state drives (SSDs). In NAND flash
memory, an erase operation applies a high voltage (e.g., > 20 V) to flash cells
for a long time (e.g., > 3.5 ms), which degrades cell endurance and potentially
delays user I/O requests. While a large body of prior work has proposed various
techniques to mitigate the negative impact of erase operations, no work has yet
investigated how erase latency should be set to fully exploit the potential of
NAND flash memory; most existing techniques use a fixed latency for every erase
operation which is set to cover the worst-case operating conditions. To address
this, we propose AERO (Adaptive ERase Operation), a new erase scheme that
dynamically adjusts erase latency to be just long enough for reliably erasing
target cells, depending on the cells' current erase characteristics. AERO
accurately predicts such near-optimal erase latency based on the number of fail
bits during an erase operation. To maximize its benefits, we further optimize
AERO in two aspects. First, at the beginning of an erase operation, AERO
attempts to erase the cells for a short time (e.g., 1 ms), which enables AERO
to always obtain the number of fail bits necessary to accurately predict the
near-optimal erase latency. Second, AERO aggressively yet safely reduces erase
latency by leveraging a large reliability margin present in modern SSDs. We
demonstrate the feasibility and reliability of AERO using 160 real 3D NAND
flash chips, showing that it enhances SSD lifetime over the conventional erase
scheme by 43% without change to existing NAND flash chips. Our system-level
evaluation using eleven real-world workloads shows that an AERO-enabled SSD
reduces read tail latency by 34% on average over a state-of-the-art technique.
