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Do some storage interfaces enable higher performance than others? Can one identify and exploit such interfaces to realize high performance in storage systems? This paper answers these questions in the affirmative by identifying nilexternality, a property of storage interfaces. A nil-externalizing (nilext) interface may modify state within a storage system but does not externalize its effects or system state immediately to the outside world. As a result, a storage system can apply nilext operations lazily, improving performance. In this paper, we take advantage of nilext interfaces to build high-performance replicated storage. We implement SKYROS, a nilext-aware replication protocol that offers high performance by deferring ordering and executing operations until their effects are externalized. We show that exploiting nil-externality offers significant benefit: for many workloads, SKYROS provides higher performance than standard consensus-based replication. For example, SKYROS offers 3x lower latency while providing the same high throughput offered by throughput-optimized Paxos. 

We present uFS, a user-level filesystem semi-microkernel. uFS takes advantage of a high-performance storage development kit to realize a fully-functional, crash-consistent, highly-scalable filesystem,with relative developer ease. uFS delivers scalable high performance with a number of novel techniques: careful partitioning of in-memory and on-disk data structures to enable concurrent access without locking, inode migration for balancing load across filesystem threads, and a dynamic scaling algorithm for determining the number of filesystem threads to serve the current workload. Through measurements, we show that uFS has good base performance and excellent scalability; for example, uFS delivers nearly twice the throughput of ext4 for LevelDB on YCSB workloads. 

The pervasive use of smart speakers has raised numerous privacy concerns. While work to date provides an understanding of user perceptions of these threats, limited research focuses on how we can mitigate these concerns, either through redesigning the smart speaker or through dedicated privacy-preserving interventions. In this paper, we present the design and prototyping of two privacy-preserving interventions: 'Obfuscator' targeted at disabling recording at the microphones, and 'PowerCut' targeted at disabling power to the smart speaker. We present our findings from a technology probe study involving 24 households that interacted with our prototypes; the primary objective was to gain a better understanding of the design space for technological interventions that might address these concerns. Our data and findings reveal complex trade-offs among utility, privacy, and usability and stresses the importance of multi-functionality, aesthetics, ease-of-use, and form factor. We discuss the implications of our findings for the development of subsequent interventions and the future design of smart speakers.