Although lateral charge spreading is considered as a dominant error source in 3D NAND flash memory, little is known about its detailed characteristics at the storage system level. From a device characterization study, we observed that lateral charge spreading strongly depends on vertically adjacent state patterns and a few specific patterns are responsible for a large portion of bit errors from lateral charge spreading. We propose a new state encoding scheme, called TailCut, which removes vulnerable state patterns by modifying encoded states. By removing vulnerable patterns, TailCut can improve the SSD lifetime and read latency by 80% and 25%, respectively.

To minimize unnecessary data movements from storage to a host, processing-in-storage (PiS) techniques, which move a compute unit to storage, have been proposed. In this position paper, we propose an extreme version of PiS solutions, called a processing-in-flash (PiF) scheme, that moves computation inside flash chips where data are physically present. As a key building block of a PiF solution, we present a novel flash chip architecture, CoX. Using a prototype PiF SSD based on CoX chips, we demonstrate that PiF-based SSDs are promising in accelerating data-intensive applications.

We propose a novel whitelist-based anti-ransomware solution called alohomora. Alohomora is based on our observation that an I/O activity of an application can be an effective abstraction level for managing I/O whitelisting. In alohomora, when a write request is sent to an SSD, its program context value (which is supported by a host CPU register) is passed to the SSD. The SSD checks if the request was pre-approved using the program context value, thus preventing ransomware from modifying files in the SSD. Our experimental results using a prototype alohomora system show that alohomora can achieve a strong security level against sophisticated ransomware attacks without degrading I/O performance.