NAND flash memory has become the dominant storage media choice in a vast majority of application scenarios. Compared to mechanical hard disks, flash offers better access performance, energy efficiency, and shock resistance. However, the unique hardware peculiarities of this technology require dedicated facilities to manage the flash space and data. The implementation of flash management facilities has alternatively been realized either at the device or host computer level. Managing flash on the device side eases integration/compatibility and increases performance in certain scenarios. However, the limited computing resources inherent to devices and the lack of higher-level file system/application information make these solutions suboptimal in many situations. Managing flash on the host allows leveraging its abundant resources, and host-side knowledge such as data access patterns can be exploited to optimize flash management, at the cost of increased host-side complexity. The pros and cons of each approach also led to the appearance of hybrid, cross-layer solutions, enabling the collaboration of different layers of the storage stack. Recently, the pressure on modern storage systems requires that an increasing amount of flash management responsibilities is offloaded to the host, and the development of application-specific cross-layer solutions: In that context, it is crucial to review these developments. In this article, we make a comprehensive survey of the host-side management technologies of flash memory, application-/system-level flash-friendly designs, and emergent applications based on flash memory.

Recently, secure data deletion or data sanitization has been identified as a key technology of storage devices to securely delete obsolete sensitive data that are no longer used. However, secure data deletion requires extra management efforts on flash memory storage devices, due to the deferred reclamation of flash blocks in many flash translation layer schemes. The emerging zoned namespace storage further exacerbates the design complexity of secure data deletion, due to the much larger size of a zone than that of a flash block. Concerning the very long latency to reset an entire zone, once some data have been written into a zone, it is very difficult to securely delete them from the zone. To achieve efficient and secure data deletion on zoned namespace storage, we propose persistence relaxation for efficient and secure sanitization (PRESS), which considers the working principle of zones of zoned namespace storage and allows the fine-grained control of deferred data persistence. As a result, applications can efficiently delete their recently written data or make the data persistent for long-term storage. Our proposal, PRESS, is evaluated through a series of experimental studies, where the results are quite encouraging.

Even though flash memory is widely used in many applications as storage due to its high performance, demands for lower storage cost and better I/O performance are still high because of the continuous growth of data. Data deduplication has the potential to address these issues by eliminating redundant writes in I/O workloads and different strategies have been proposed to improve its efficiency. However, existing designs mainly rely on time-consuming SHA-1 fingerprint scheme or byte-by-byte comparison to identify duplicate data, and these methods cause much overhead and become a bottleneck in data deduplication. To tackle this issue, we propose the hierarchical fingerprint scheme (HF-Dedupe) to improve the efficiency of data deduplication for flash-based storage systems. By leveraging multiple levels of light-weight hashes in the fingerprint, our design only takes the minimal effort to distinguish different data in write traffic. In order to evaluate our design, a series of experiments were conducted based on trace-driven simulations. Compared with other designs, the experimental results show that HF-Dedupe further reduces the deduplication time by 34.76%-65.02 % while retaining high deduplication ratio, and therefore achieves the most improvement to overall I/O performance.

Modern nonvolatile memories (NVMs) are widely recognized as energy-efficient replacements of classical memory/storage media, such as SRAM, DRAM, and mechanical hard disk. Among the popular NVMs, the skyrmion racetrack memory (SK-RM) is well known for its high storage density and unique supports of insert/delete operations. However, the existing algorithms designed for classical media might experience serious performance degradation when working on the SK-RM, due to the distinct characteristics of SK-RM. Thus, the existing algorithms should be redesigned to adapt to the brand-new memory model based on the SK-RM, so as to fully reveal the potentials of SK-RM. In particular, many existing algorithms tend to access the in-memory data in a random-hopping fashion, which generates many time-consuming shift operations of SK-RM. It is therefore crucial for the existing algorithms to eliminate unnecessary shift operations of SK-RM to boost the performance of the algorithms. In many modern applications, such as multimedia and data analysis, it is a common operation to process two or more arrays/vectors of data to perform certain computation tasks. In the arrays/vectors, an appropriate data placement strategy is critical for avoiding unnecessary shift operations of SK-RM. The observation thus motivates this work in proposing a recursive back-to-back data placement manner to effectively reduces the shift operations of SK-RM. To demonstrate the back-to-back data placement, we take sorting algorithms as a case study, and propose a novel shift-limited sorting algorithm for SK-RM. Analytical studies show that the shift-limited sort effectively enhances the time complexity of classical merge sort from O(dn lg n) to O(n lg n), where d is the bit distance between adjacent access ports on the nanotracks of the SK-RM. After that, the efficacy of the proposed shift-limited sort is then verified by experimental studies, where the results are encouraging.