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Study of Effective Valid Page Tracking Methods in Mobile Flash Storage without DRAM
http://doi.org/10.5626/JOK.2025.52.5.357
Mobile systems, commonly use flash-based storage devices like Universal Flash Storage (UFS). These devices are designed with a small form factor and operate under limited power and budget constraints, often lacking large internal DRAM. As a result, they rely on small SRAM to run the Flash Translation Layer (FTL). This limitation makes it difficult to manage metadata, such as address mapping tables and the Valid Page Bitmap related to garbage collection (GC), within SRAM. Managing the Valid Page Bitmap in flash memory poses challenges due to performance degradation from significant metadata I/O overhead. This paper proposes an efficient method for tracking valid pages within specific blocks by managing L2P segment bitmaps per block. This approach minimizes the metadata access overhead during valid page tracking, leading to improved performance. Evaluation results indicate up to an 83% reduction in latency for finding valid pages compared to existing methods, particularly with a 128KB I/O unit.
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.
Optimized Design of Filesystems for Unikernel
Kyeong Woon Cho, Hyo Kyeong Ban
http://doi.org/10.5626/JOK.2024.51.5.389
Unikernel is a special-purpose kernel optimized for single applications and services. Compared to general-purpose kernels, its advantages include fast boot time, small memory footprint, high performance, and security. Unikernel applications attempt to maintain compatibility with the runtime environment of the general-purpose kernel and are used in binary or source-compatible form with legacy applications. Most existing unikernel projects implemented filesystem APIs with a priority on running applications rather than performance optimizations. Accordingly, it is a common practice to deploy a general-purpose file system naively or to introduce a host filesystem dependent method. In this paper, we discuss the design of unikernel file systems taking into account the purpose of unikernel, i.e., ensuring optimized performance with minimal system resources while maintaining security. Specifically, we analyze the performance and memory requirements for file systems supported by major unikernels through micro-benchmarks and suggest file system design guidelines to provide optimized performance and security.
Storage Trie Optimization Based on Ethereum Transaction Data
http://doi.org/10.5626/JOK.2024.51.2.110
Interest in blockchain has grown with the increased usage of Ethereum, thus the blockchain state data has exploded, making it difficult for users to participate in the network. In this paper, we propose a method of optimizing the storage trie, which accounts for a significant portion of state data, based on pas transaction data of real Ethereum. By deleting storage trie that never appeared during 1 million blocks from a massive 14 million block storage tire, we reduced the storage space by 19.6%, which is 10.8GB. Based on the research results of this paper, it is expected that we can propose a more effective storage trie optimization based on data.
CSDVirt: An Emulator for Computational Storage Device
Ilkueon Kang, Jaehoon Shim, Jin-Soo Kim
http://doi.org/10.5626/JOK.2024.51.1.1
Since Computational Storage Device (CSD) concept was proposed, various forms of CSDs have been presented in both academia and industries. The standardization of CSD interfaces is currently undergoing, but they are still in a very early stage. As a result, the existing CSD proposals lack uniformity in interfaces and internal device architectures. This has led to significant engineering efforts for CSD research. In this paper, we propose CSDVirt to facilitate the CSD research and provide an environment similar to actual devices. CSDVirt is an emulator that offers CSD functionalities using NVMeVirt. With CSDVirt, the characteristics of various workloads on CSDs can be evaluated easily.
Addressing Write-Warm Pages in OLTP Workloads
Kyong-Shik Lee, Mijin An, Sang-Won Lee
http://doi.org/10.5626/JOK.2023.50.11.1002
One of the most important purposes of buffer management policies is to cache frequently accessed data in the buffer pool to minimize disk I/O. However, even if frequently referenced pages are effectively stored, a small number of pages can still result in excessive disk I.O. This is because of write-warm pages, which are repeatedly fetched and evicted from the buffer pool. In this paper, we introduce a “(Write-)Warm Page Thrashing” problem and confirm the existence of write-warm pages. Specifically, we found that 10% of flushed pages accounted for 41% of writes. This could degrade the performance, particularly for flash memory devices with slow write speeds. Therefore, a new buffer management policy is required to detect and prevent such thrashing problem.
Distributed Storage System for Reducing Write Amplification on Non-Volatile Memory
http://doi.org/10.5626/JOK.2020.47.2.129
Recently, research on non-volatile memory, such as 3DXpoint, in distributed storage systems has received considerable interest from both academia and industry. However, in order to utilize these state-of-the-art non-volatile memory devices effectively in distributed storage systems, there is a need for improvements in traditional architectures of HDD/SSD-based storage systems. This is because current distributed storage system structures use a dedicated space for journaling to make up for slow storage performance. Also, considering the performance characteristics of non-volatile memory, which are similar to that of DRAM, current distributed storage system structures are not only inefficient in terms of overall performance but also cause write amplification. In this paper, we propose an architecture that mitigates the effects of write amplification in non-volatile memory-based distributed storage systems. To evaluate the proposed architecture and scheme, we have conducted diverse experiments in a CEPH storage system environment. Through these experiments, we have confirmed that the DAXNJ structure proposed in this paper decreases write amplification by 61% during 1M object write operations and increases the overall system performance by 15%.
An Efficient SLC-buffer Management Scheme for TLC NAND Flash-based Storage
Kirock Kwon, Dong Hyun Kang, Young Ik Eom
http://doi.org/10.5626/JOK.2018.45.7.611
In recent years, almost all consumer devices have adopted NAND flash storage as their main storage, and their performance and capacity requirements are getting higher. To meet these requirements, many researchers have focused on combined SLC-TLC storage consisting of high-speed SLC and high-density TLC. In this paper, we redesign the internal structure of the combined SLC-TLC storage to efficiently manage the SLC region inside the storage and propose a scheme that improves the performance of the storage by employing the I/O characteristics of file system journaling. We implemented our scheme on the real storage platform, the OpenSSD jasmine board, and compared it with the conventional techniques. Our evaluation results show that our technique improves the storage performance by up to 65%, compared with the conventional techniques.
An Analysis of the Overhead of Multiple Buffer Pool Scheme on InnoDB-based Database Management Systems
Yongju Song, Minho Lee, Young Ik Eom
The advent of large-scale web services has resulted in gradual increase in the amount of data used in those services. These big data are managed efficiently by DBMS such as MySQL and MariaDB, which use InnoDB engine as their storage engine, since InnoDB guarantees ACID and is suitable for handling large-scale data. To improve I/O performance, InnoDB caches data and index of its database through a buffer pool. It also supports multiple buffer pools to mitigate lock contentions. However, the multiple buffer pool scheme leads to the additional data consistency overhead. In this paper, we analyze the overhead of the multiple buffer pool scheme. In our experimental results, although multiple buffer pool scheme mitigates the lock contention by up to 46.3%, throughput of DMBS is significantly degraded by up to 50.6% due to increased disk I/O and fsync calls.
A Secure and Practical Encrypted Data De-duplication with Proof of Ownership in Cloud Storage
Cheolhee Park, Dowon Hong, Changho Seo
In cloud storage environment, deduplication enables efficient use of the storage. Also, in order to save network bandwidth, cloud storage service provider has introduced client-side deduplication. Cloud storage service users want to upload encrypted data to ensure confidentiality. However, common encryption method cannot be combined with deduplication, because each user uses a different private key. Also, client-side deduplication can be vulnerable to security threats because file tag replaces the entire file. Recently, proof of ownership schemes have suggested to remedy the vulnerabilities of client-side deduplication. Nevertheless, client-side deduplication over encrypted data still causes problems in efficiency and security. In this paper, we propose a secure and practical client-side encrypted data deduplication scheme that has resilience to brute force attack and performs proof of ownership over encrypted data.
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