Lee, Seungjin

Unlike traditional block-based SSDs, Zoned Namespace (ZNS) SSDs expose storage through the zoned block interface, completely eliminating the need for in-device garbage collection (GC) and relinquishing this responsibility to applications. As a result, application-aware data placement decisions give the opportunity for applications on the host to perform efficient GC. Meanwhile, RocksDB for ZNS SSD places data with similar invalidation times (lifetimes) in the same zone through ZenFS (a user-level file system) using the Lifetime-based Zone Allocation algorithm (LIZA), and minimizes the GC overhead of valid data copy when reclaiming a zone. However, LIZA, which allocates zones by predicting the lifetime of each SSTable according to the level of the hierarchical structure of the LSM-tree, is very inefficient in minimizing the write amplification (WA) problem due to inaccurate predictions of SSTable lifetimes. Instead, based on our observation that the deletion time of SSTables in the LSM-tree is solely determined by the compaction process, we propose a novel Compaction-Aware Zone Allocation algorithm (CAZA) that allows the newly created SSTables to be deleted together after merging in the future. CAZA is implemented in RocksDB's ZenFS and our extensive evaluations show that CAZA significantly reduces the WA overhead compared to LIZA.

This paper demonstrates that SSDs, which perform device-level versioning, can be exposed to data tampering attacks when the retention time of data is less than the malware's dwell time. To deal with that threat, we propose SGX-SSD, a SGX-based versioning SSD which selectively preserves file history based on the given policy. The proposed system adopts Intel SGX to implement the version policy management system that is safe from high-privileged malware. Based on the policy, only the necessary data is selectively preserved in SSD that prevents files with less priority from wasting space and also ensures the integrity of important files.

This paper presents a wireless temperature sensor that uses a GaAs solar cell as a wireless transmitter of information. Transmission of information with a solar cell is possible by modulating the luminescent radiation emitted by the solar cell. This technique, dubbed Optical Frequency Identification or OFID, was recently reported in the literature and in this work is used to transmit temperature measurements wirelessly. The hardware design of an OFID temperature sensor tag and its corresponding reader is described. A prototype of the proposed sensor was built as a proof of concept. Experimental results demonstrate wireless data transmission at a distance of 1 m distance and at a bit rate of 1200 bps. The wireless temperature sensor has a maximum error of 0.39°C (after calibration) with respect to a high-precision temperature meter.

A new wireless communication approach that employs solar cells as receivers and transmitters of information has been recently proposed [1,2]. This approach, which has been dubbed Optical Frequency Identification (OFID) for its analogy with Radio Frequency Identification (RFID), exploits the infrared luminescent radiation emitted by high-efficiency solar cells, such as GaAs solar cells, when excited by light (photo-luminescence or PL) or an electrical current (electroluminescence or EL). In OFID, the luminescent emissions of a solar cell are modulated by varying the voltage across the solar cell. Binary On-Off as well as multi-level modulations are possible in this scheme. The solar cell can also be used to receive information encoded optically by virtue of its photo-transduction property. Finally, in an OFID system the solar cell is also used for its intended purpose, which is to harvest radiant optical energy.