• Journal of KIISE:Computing Practices and Letters
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• v.15 no.12
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• pp.958-962
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• 2009

Flash memory, which replaces hard disk recently, has different physical characteristics with hard disk. For the performance of flash memory based storage system, many researches over OS and file system layers has been doing. In this paper, we propose the architecture of flash memory based storage which uses information of page invalidation when file deletion occurs from upper layer. Also, we evaluate the performance of proposed system. Proposed system effectively increases IO performance by using page invalidation information to block merge and wear leveling algorithms.

• The Journal of the Korea Contents Association
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• v.21 no.7
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• pp.157-163
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• 2021

A single write operation in a file system can modify multiple data, but these changes in the file system are not atomically written to disk. Thus, for the consistency of the file system, conventional journaling guarantees crash consistency instead of sacrificing the system performance. It is known that using non-volatile memory as a journal space can alleviate performance degradation due to low latency and byte-level accessibility of non-volatile memory. However, none of the journaling techniques considering non-volatile memory provide scalability. In this paper, journal space on non-volatile memory is divided into multiple regions for scalable journaling, thus dispersing concentrated operations in one region. Second, the journal area-specific operator structure is used to accelerate data write operations to storage devices. We apply the proposed technique to JFS to evaluate it on multi-core servers equipped with high-performance storage devices. The evaluation results show that the proposed technique performs better than the existing technique of the NVM-based journaling file system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.115-122
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• 2004

This paper describe the implementation or the boot loader for the boot system using of memory card. This boot roader consist of the system initialization, CF card checking, CF memory card checking, file system and the program relocator. This boot loader increase the system stability with program consistency checking algorithm in the read phase from the CF memory card. And this system have the compatibility in CF memory card file system, so system manufacturing productivity increase.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.2
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• pp.241-245
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• 2008

Non-volatile RAM (NVRAM) has both characteristics of nonvolatility and byte addressability. In order to efficiently exploit this NVRAM in the file system layer, we proposed the MiNV (Metadata in NVram) file system in our previous research. MiNV file system maintains all the metadata in NVRAM while storing file data in NAND Flash memory. In this paper, we experimentally analyze the efficiency for the execution of garbage collection in the MiNV file system. Also, we quantify the file system performance gains obtained from efficient garbage collection. Experimental results show that garbage collection on the MiNV file system executes more efficiently that on YAFFS even though these file systems adopt exactly the same garbage collection policy. Specifically, the MiNV file system invokes the aggressive garbage collection mechanism less frequently than YAFFS. Additionally, the MiNV file system postpones the first execution of the aggressive garbage collection mechanism in our experiments. From the experiments, we verify that the efficiency of garbage collection leads to performance improvements of the MiNV file system.

• The Journal of the Korea Contents Association
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• v.20 no.8
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• pp.368-374
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• 2020

Journaling file systems (JFS) manage changes of file systems not yet committed in a data structure known as a journal to restore the file system in the event of an unexpected failure. Extra write operations required for journaling negatively affect the performance of JFS. The high-performance and byte-addressable non-volatile memory (NVM) was expected to easily mitigate these performance problems by providing NVM space as journal storage. However, even with such non-volatile memory technologies, performance problems still arise due to scalability problems inherent in processing transactions of JFS. To solve this problem, we proposes a technique for processing file system transactions for scalable performance. To this end, lock-free data structures are used and multiple I/O requests are allowed to simultaneously be processed on high-performance storage devices with multiple I/O channels. We evaluate the file system with the proposed technique by comparing the original ext4 file system and the recent proposed NVM-based journaling file system on a multi-core server, and experimental results show that our file system has better performance (up-to 2.9/2.3 times) than the original ext4 file system and the recent NVM-based journaling file system, respectively.

• Journal of KIISE
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• v.43 no.8
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• pp.841-847
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• 2016

As network technology advances, a larger number of devices are connected through the Internet. Recently, cloud storage services are gaining popularity, as they are convenient to access anytime and anywhere. Among cloud storage services, object storage is the representative one due to their characteristics of low cost, high availability, and high durability. One limitation of object storage services is that they can access data on the cloud only through the HTTP-based RESTful APIs. In our work, we resolve this limitation with the in-memory file system which provides a POSIX interface to the file system users and communicates with cloud object storages with RESTful APIs. In particular, our flush mechanism is compatible with existing file systems, as it is based on the swap mechanism of the Linux kernel. Our in-memory file system backed by cloud storage reduces the performance overheads and shows a better performance than S3QL by 57% in write operations. It also shows a comparable performance to tmpfs in read operations.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.9
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• pp.615-625
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• 2006

Nonvolatile memory technology is evolving continuously and commercial products such as FeRAM and PRAM are now challenging their markets. As NVRAM has properties of both memory and storage, it can store persistent data objects while allowing fast and random access. To utilize NVRAM for general purpose storing of frequently updated data across power disruptions, some essential features of the file system including naming, recovery, and space management are required while exploiting memory-like properties of NVRAM. Conventional file systems, including even recently developed NVRAM file systems, show very low space efficiency wasting more than 50% of the total space in some cases. To efficiently utilize the relatively expensive NVRAM, we design and implement a new extent-based space-thrifty file system, which we call NEBFS (NVRAM Extent-Based File System). We analyze and compare the space utilization of conventional file systems with NEBFS and validate the results with experimental results observed from running the file system implementations on a system with actual NVRAM installed as well as on systems emulating NVRAM. We show that NEBFS has high space efficiency compared to conventional file systems.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.27 no.5
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• pp.1013-1022
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• 2017

Windows hibernation is a function that stores data of physical memory on a non-volatile media and then restores the memory data from the non-volatile media to the physical memory when the system is powered on. Since the hibernation file has memory data in a static state, when the attacker collects it, key information in the system's physical memory may be leaked. Because Windows does not support protection for hibernation files only, we need to protect the memory that is written to the hibernate file. In this paper, we propose a method to encrypt the physical memory data in the hibernation file to protect the memory data of the processes recorded in the hibernation file. Hibernating procedure is analyzed to encrypt the memory data at the hibernating and the encryption process for hibernation memory is implemented to operate transparently for each process. Experimental results show that the hibernation process memory encryption tool showed about 2.7 times overhead due to the crypt cost. This overhead is necessary to prevent the attacker from exposing the plaintext memory data of the process.

• The KIPS Transactions:PartA
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• v.12A no.7 s.97
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• pp.571-582
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• 2005

NAND flash memory has advantages of non-volatility, little power consumption and fast access time. However, it suffers from inability that dose not provide to update-in-place and the erase cycle is limited. Moreover, the unit of read and write operations is a page. A NAND flash file system called YAFFS has been proposed. But YAFFS has several problems to be addressed. In this paper, the Reliable Flash File System(RFFS) for NAND flash memory is designed and evaluated. In designing a file system the following four issues must be considered in particular for the design: (i) to minimize a repairing time when the system fault occurs, (ii) to balance the number of block erase operations by offering wear leveling policy, and (iii) to reduce turnaround time of memory operations by reducing the amount of data written. We demonstrate and evaluate the performance of the proposed schemes.

• Journal of Digital Contents Society
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• v.14 no.2
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• pp.247-254
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• 2013

Storage Class Memory(SCM), such as PRAM, FRAM and MRAM, are expected to be comparable to DRAM in terms of access speed and to Flash memory in terms of capacity in a near future. In this paper, assuming that not only the secondary storage (HDD or Flash memory) but also the primary memory (DRAM) will be replaced by SCM in the future computer systems, we propose an efficient file access framework for the SCM based computer systems. The proposed framework do not assign exclusive area in the SCM to the file system and uses various memory-related techniques, such as unified data access path, zero-copy data read using file mapping, copy-on-write, and multiple page pre-faulting for file management. Based on the preliminary experimental results, we could conclude that the proposed framework can be an efficient baseline for designing a new operating system for the SCM based computer systems.