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This paper proposes a new approach, called file concealer (FC), to conceal files in a computer system. FC modifies metadata about a file in NTFS (New Technology File System) to hide the file. Unlike traditional hooking methods which can be easily detected by antivirus software, experimental results show that it is difficult for antivirus software to detect the files hidden by FC. Moreover, to enhance the concealment capability of FC, FC also rearranges the order of some data sectors of a hidden file. As a result, even if another person finds the original sectors used by the hidden file, it is difficult for him to recover the original content of the hidden file. Experimental results show that even data recovery tools cannot restore the content of a hidden file. All information that is required to restore a hidden file is stored in a file, called recovery file hereafter. When a user uses FC to hide a file, the user can specify any file as a host file, such as an image file, to which the recovery file will be appended. As a result, the user can easily restore a hidden file; however, it is difficult for other person to detect or restore the hidden file and the related recovery file.

Large-scale small file storage for original pages degrades performance of search engines. In this paper, we first analyze the disadvantages of the existing EXT3 file system in accessing small files. Then, the rate and speed of compression algorithms are verified to choose a proper storage compression algorithm. Meanwhile, we design an original page oriented file organization structure and a read---write query tree to store the large-scale small files which need no modification. The accessing response time and disk space waste are remarkably decreased when search engines use these techniques to store original-page small files.

Parallel file systems are experiencing more and more applications from various fields. Various applications have different I/O workload characteristics, which have diverse requirements on accessing storage resources. However, parallel file systems often adopt the "one-size-fits-all" solution, which fails to meet specific application needs and hinders the full exploitation of potential performance. This paper presents a framework to enable dynamic file I/O path selection with fine granularity at runtime. The framework adopts a file handle-rich scheme to allow file systems choose corresponding optimizations to serve I/O requests. Consistency control algorithms are proposed to ensure data consistency while changing optimizations at runtime. One case study on our prototype shows that choosing proper optimizations can improve the I/O performance for small files and large files by up to 40 and 64.4 %, respectively. Another case study shows that the data prefetch performance for real-world application traces can be improved by up to 193 % by selecting correct prefetch patterns. Simulations in large-scale environment also show that our method is scalable and both the memory consumption and the consistency control overhead can be negligible.

Distributed cryptographic file systems enable file sharing among their users and need the adoption of a key management scheme for the distribution of the cryptographic keys to authorized users according to their specific degree of trust. In this paper we describe the architecture of a basic secure file sharing facility relying on a multi-party threshold-based key-sharing scheme that can be overlaid on top of the existing stackable networked file systems, and discuss its application to the implementation of distributed cryptographic file systems. It provides flexible access control policies supporting multiple combination of roles and trust profiles. A proof of concept prototype implementation within the Linux operating system framework demonstrated its effectiveness in terms of performance and security robustness.

The performance of metadata processing in large distributed file systems currently presents larger challenges than scaling of data throughput. The paper presents a novel, distributed benchmark called DMetabench for measuring the performance of metadata operations. DMetabench runs in environments with potentially thousands of nodes and allows an assessment of the scalability of metadata operations. Additionally, precise run-time performance data is preserved which allows for a better understanding of performance artifacts. Example results from production file systems are provided and discussed. Possible applications of knowledge about metadata performance scaling include the choice of an optimal parallelization strategy for metadata-intensive workloads in a specific runtime environment.

Parallelism in file systems is obtained by using several independent server nodes supporting one or more secondary storage devices. This approach increases the performance and scalability of the system, but a fault in one single node can stop the whole system. To avoid this problem, data must be stored using some kind of redundant technique, so any data stored in a faulty element can be recovered. Fault tolerance can be provided in I/O systems by using replication or RAID based schemes. However, most of the current systems apply the same technique for all files in the system. This paper describes the fault tolerance support provided by Expand, a parallel file system based on standard servers. This support can be applied to other parallel file systems with many benefices: fault tolerance at file level, flexible definition of fault tolerance scheme to be used, possibility to change the fault tolerant support used for a file, etc.