How to enable software isolation and boost system performance with sub-block erase over 3D flash memory.

The write amplification problem deteriorates as the block size of modern flash-memory chips keeps increasing. Without the careful garbage collection, significant live-page copying might even worsen the reliability problem, that is already severe to 3D flash memory. In this work, we propose a sub-block erase design to not only alleviate the write amplification problem by reducing livepage copying but also improve the system reliability with a software isolation strategy. In particular, sub-blocks are carefully allocated to satisfy write requests so as to reduce disturbance by using free or invalid sub-blocks as isolation layers among sub-blocks, without additional hardware cost and capacity loss. A series of experiments were conducted to evaluate the capability of the proposed design. The results show that the proposed design is very effective in improving the system performance by reducing garbage collection overheads and in improving the device reliability/lifetime.