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Managing DISCARD Commands in F2FS File System for Improving Lifespan and Performance of SSD Devices
Jinwoong Kim, Donghyun Kang, Young Ik Eom
http://doi.org/10.5626/JOK.2024.51.8.669
The DISCARD command is an interface that helps improve the lifespan and performance of SSDs by informing the SSD devices about invalid file system blocks. However, in the F2FS file system, the DISCARD command is only sent to the SSD during idle time, which limits the potential for improving lifespan and performance. In this paper, we propose an EPD scheme to efficiently transfer DISCARD commands during short idle times, as well as a seg-ment allocation scheme called PSA, which replaces DISCARD commands with overwrite commands. To evaluate the effectiveness of these proposed schemes, we conducted several experiments using various workloads to verify the lifespan and performance of real SSD devices. The results showed that the proposed schemes can improve the write amplification factor (WAF) by up to 40% and throughput by up to 160%, when compared to the traditional F2FS file system.
Integrated Host-SSD Mapping Table Cache Management Techniques for Improving Performance of a Mobile Storage Device
Yoona Kim, Inhyuk Choi, Sungjin Lee, Jihong Kim
http://doi.org/10.5626/JOK.2023.50.11.924
As the size of a storage device gradually increases, the demand for on-device memory capacity required for managing the address mapping translation of a NAND flash-based storage device increases. The on-device memory capacity of a mobile storage device, Universal Flash Storage (UFS), does not increase due to H/W and cost constraints, making it challenging to manage the increased address translation table. To resolve the problem, Host Performance Booster (HPB), which borrows host-side DRAM memory to load portions of the address translation table was introduced. In this paper, we demonstrate that the HPB-enabled system does not work in an integrated manner with the device-side SRAM, therefore wasting the given memory resource. We propose integrated mapping table management techniques that consider the distinctive features of each cache layer. By adopting these techniques, we aim to minimize wasted cache resources, reduce storage latency, and prevent unnecessary degradation of the storage lifetime. Based on the evaluation results, the cache hit ratio is improved by 5% while the wasted memory resource is reduced by 95%, and the number of device-side garbage collections is reduced by 43% compared to the baseline scheme.
ESP: Improving Performance and Lifetime of High-Capacity 3D Flash Storage Using an Erase-Free Subpage Programming Technique
http://doi.org/10.5626/JOK.2023.50.1.1
Recent high-capacity 3D NAND flash devices have large page sizes. Although large pages are useful in increasing flash capacity, they can degrade both the performance and lifetime of flash storage systems when small writes are dominant. We propose a new NAND programming scheme, called erase-free sub-page programming (ESP), which allows the same page to be programmed multiple times for small writes without the intervention of the erase operation. By avoiding internal fragmentation, the ESP scheme reduces the overhead of garbage collection for large-page NAND storage. Based on the proposed ESP scheme with an adaptive retention management technique, we implemented an ESP-aware FTL(subFTL) and performed comprehensive evaluations using various benchmarks and workloads. The experimental results showed that an ESP-aware FTL could improve the IOPS and lifetime by up to 74% and 177%, respectively.
ESS Operation Scheduling Scheme Using LSTM for Peak Demand Reduction
Yeongung Seo, Seungyoung Park, Myungjin Kim, Sungbin Lim
http://doi.org/10.5626/JOK.2019.46.11.1165
In recent years, blackouts have become more likely in South Korea as the peak demand has sharply increased. In order to address this issue, an energy storage system (ESS) operation scheduling technique has been investigated for its ability to reduce the peak demand by utilizing the power stored in the ESS. If the power demand information is known in advance, an optimal ESS operation scheduling technique can be applied in consideration of both the power stored in the ESS and the power demand to be generated in the future. However, it is difficult to predict the peak demand in advance because it only occurs in a relatively short time period, and the instance of its occurrence differs substantially from day-to-day. Therefore, it is very difficult to implement an optimal ESS operation scheduling technique that requires exact information on power demands in advance. Thus, in this paper, we proposed an ESS operation scheduling method with which to reduce the peak demand by using only historical power demands. Specifically, we employed a long short-term memory (LSTM) network and trained it using the historical power demands and their corresponding optimal ESS discharge powers. Then, we applied the trained network to approximate the optimal ESS operation scheduling. We showed the validity of the proposed method through computer simulations using historical power demand data from four customers. In particular, it was shown that the proposed scheme reduced the peak demand per year by up to about 82.42% compared to the optimal scheme that is only feasible when the exact future power demands are available.
Improving Performance of Flash Storage Using Restricted Copyback
Duwon Hong, Seulgi Shin, Jihong Kim
http://doi.org/10.5626/JOK.2019.46.8.726
In case of modern flash-based SSDs, the performance overhead of internal data migrations is dominated by the data transfer time and not by the flash program time as in old SSDs. In order to mitigate the performance impact of data migrations, we propose rcopyback, a restricted version of copyback. Rcopyback works in a manner similar to the original copyback except that only n consecutive copybacks are allowed. By limiting the number of successive copybacks, the version guarantees internal migration of data using rcopyback without any reliability problem. In order to take a full advantage of rcopyback, we developed a rcopyback-aware FTL, rcFTL, which intelligently decides whether rcopyback should be used or not by exploiting varying host workloads. Our evaluation results show that rcFTL can improve the overall I/O throughput by 54% on average over an existing FTL which does not use copybacks.
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