An Active Method to Mitigate the Long Latencies for HostAware Shingle Magnetic Recording Drives Shingled Magnetic Recording (SMR) is one of the most promising techniques that satisfy the evergrowing storage volume demands. By overlapping tracks, SMR enormously improves the storage area density, which in turn brings higher storage volumes. However, SMR sacrifices the random write performance for better storage volumes. Current SMR drives propose to remedy this problem by employing an indrive persistent cache to temporally store incoming writes and migrate them to their disk destinations later on. Unfortunately, cleaning processes for the persistent cache takes up to tens of seconds, and the unpredictable timing of these timeconsuming operations chokes normal requests and drastically degrades SMR drive performance. In this paper, we propose to remedy this issue by proactively freeing the persistent cache space so that keeping these lengthy processes transparent with regards to normal requests, therefore reducing the long tails and delivering steady and predictable performance for SMR drivebased storage systems. We prototype our design as a HostAware SMR drive aware userspace file system, AM FS, and evaluate it on the real HASMR drive with libzbc. Evaluations results show that AM FS reduces the long tails of HASMR drives.

Hybrid Storage System to Achieve Efficient Use of Fast Memory Area Hybrid storage techniques are useful methods to improve the cost performance for inputoutput (IO) intensive workloads. These techniques choose areas of concentrated IO accesses and migrate them to an upper tier to extract as much performance as possible through greater use of upper tier areas. Automated tiered storage with fast memory and slow flash storage (ATSMF) is a hybrid storage system situated between nonvolatile memories (NVMs) and solidstate drives (SSDs). ATSMF aims to reduce the average response time for IO accesses by migrating areas of concentrated IO access from an SSD to an NVM. When a concentrated IO access finishes, the system migrates these areas from the NVM back to the SSD. Unfortunately, the published ATSMF implementation temporarily consumes much NVM capacity upon migrating concentrated IO access areas to NVM, because its algorithm executes NVM migration with high priority. As a result, it often delays evicting areas in which IO concentrations have ended to the SSD. Therefore, to reduce the consumption of NVM while maintaining the average response time, we developed new techniques for making ATSMF more practical. The first is a queue handling technique based on the number of IO accesses for NVM migration and eviction. The second is an eviction method that selects only writeaccessed partial regions in finished areas. The third is a technique for variable eviction timing to balance the NVM consumption and average response time. Experimental results indicate that the average response times of the proposed ATSMF are almost the same as those of the published ATSMF, while the NVM consumption is drastically lower.