Directory Operations Research Articles

CFFS: A Persistent Memory File System for Contiguous File Allocation With Fine-Grained Metadata

Extensive research on persistent memory (PM)-aware file systems has led to the development of numerous methods for improving read/write throughput. In particular, accessing or modifying file contents in a similar manner to the memory operations through <i>mmap</i> is a common approach. We designed a file system, CFFS (Contiguous File Allocation with Fine-Grained Metadata File System), to rapidly allocate PM pages to upper layer applications for <i>mmap</i> and to alleviate page fault overheads due to <i>mmap</i>. We optimized the physical contiguity of files in PM to reduce file fragmentation and increase fragment alignment with the goal of reducing software overhead. To achieve this goal, we implemented greedy-based buddy systems and implicit preallocation with a not-most-recently-used (NMRU) policy based on our overall page allocation strategy of considering not only the spatial but also the temporal locality of file access patterns. Furthermore, for efficient and atomic metadata operations, we fully leveraged the byte-addressable property of PM to design fine-grained metadata. CFFS adopts persistent doubly linked lists for directory operations to identify and recover from inconsistencies caused by system failures, doing so without using traditional log mechanisms. In experiments, CFFS showed superior page allocation performance to EXT4-DAX and NOVA did under different PM fragmentation levels. Our allocation algorithm also reduced the cost of page faults for frequently appended files. Finally, CFFS&#x2019;s lightweight directory operations performed excellently in creating and deleting files of various quantities. In summary, the main contribution of the paper is proposing an efficient page allocation algorithm to improve the performance of subsequent <i>mmaps</i>, based on the strategy of considering not only the spatial but also the temporal locality of file access patterns in PM file systems. Another contribution was the fine-grained and log-free method for atomic directory operations.

A Highly Reliable Metadata Service for Large-Scale Distributed File Systems

Many massive data processing applications nowadays often need long, continuous, and uninterrupted data accesses. Distributed file systems are used as the back-end storage to provide the global namespace management and reliability guarantee. Due to increasing hardware failures and software issues with the growing system scale, metadata service reliability has become a critical issue as it has a direct impact on file and directory operations. Existing metadata management mechanisms can provide fault tolerance capability to some level but are inadequate. They often have limitations in system availability, state consistence, and performance overhead and lack an effective mechanism to offer metadata reliability. This paper introduces a novel highly reliable metadata service to address these issues in large-scale file systems. Different from traditional strategies, this proposed reliable metadata service adopts a new active-standby architecture for fault tolerance and uses a holistic approach to improve file system availability. A new shared storage pool (SSP) is designed for transparent metadata synchronization and replication between active and standby servers. Based on the SSP, a new policy called multiple actives multiple standbys (MAMS) is presented to perform metadata service recovery in case of failures. A new global state recovery strategy and a smart client fault tolerance mechanism are achieved to maintain the continuity of metadata service. We have implemented such highly reliable metadata service in a prototype file system CFS (Clover file system) and conducted extensive tests to evaluate it. Experimental results confirm that it can significantly improve file system reliability with fast failover under different failure scenarios while having negligible influence on performance. Compared with typical reliability designs in Hadoop Avatar, Hadoop HA, and Boom-FS file systems, the mean-time-to-recovery (MTTR) with the highly reliable metadata service was reduced by 80.23, 65.46 and 28.13 percent, respectively.

Forensic analysis of B-tree file system (Btrfs)

This paper identifies forensically important artifacts of B-tree file system (Btrfs), analyses changes that they incur due to node-balancing during file and directory operations, and based on the observed file system state-change proposes an evidence-extraction procedure. The findings suggested that retrieving forensic evidence in a fresh B-tree file system is difficult, the probability of evidence-extraction increases as the file system ages, internal nodes are the richest sources of forensic data, degree of evidence-extraction depends upon whether nodes are merged or redistributed, files with size less than 1 KB and greater than 4 KB have highest chances of recovery, and files with size 3–4 KB have least chances of recovery.

Paginas Amarelas

This case serves as a foundation for student discussion of the estimation of required rates of return (ROR) on investments in emerging markets. An associate in J.P. Morgan's Latin America M&amp;A department (mergers and acquisitions) is assigned the task of valuing the telephone directory operations (“paginas amarelas” means “yellow pages”) of a large Brazilian conglomerate. All cash flows have been converted to U.S. dollars, and present values computed for various discount rates. The remaining step is to determine the appropriate target rate of returns for dollar flows originating in Argentina, Brazil, and Chile. The capital asset pricing model (CAPM) is used along with a political risk premium and country beta. The necessary figure work is comparatively light, leaving the student time to reflect on the need for various adjustments in estimating crossborder rates of return.

AT&amp;T Inc

AbstractCommunications (MIC: SIC: 4813 NAIC: 517110)AT&amp;T is a holding company providing telecommunications services. As of Dec 31 2007, Co. was divided into four reportable segments: wireline, which consisted of three product‐based categories: voice, data and other; wireless, which provided a range of nationwide wireless voice communications services in a variety of pricing plans, including postpaid and prepaid service plans; advertising &amp; publishing, which included its directory operations that published Yellow and White Pages directories and sold directory and Internet‐based advertising; and other, which included operations from Sterling, its business integration software and services subsidiary, as well as corporate and other operations.

AT&amp;T Inc

AbstractCommunications (MIC: SIC: 4813 NAIC: 517110)AT&amp;T is a holding company providing telecommunications services. As of Dec 31 2007, Co. was divided into four reportable segments: wireline, which consisted of three product‐based categories: voice, data and other; wireless, which provided a range of nationwide wireless voice communications services in a variety of pricing plans, including postpaid and prepaid service plans; advertising &amp; publishing, which included its directory operations that published Yellow and White Pages directories and sold directory and Internet‐based advertising; and other, which included operations from Sterling, its business integration software and services subsidiary, as well as corporate and other operations.

AT&amp;T Inc

AbstractCommunications (MIC: 10.1 SIC: 4813 NAIC: 517110)AT&amp;T is a holding company providing telecommunications services. As of Dec 31 2007, Co. was divided into four reportable segments: wireline, which consisted of three product‐based categories: voice, data and other; wireless, which provided a range of nationwide wireless voice communications services in a variety of pricing plans, including postpaid and prepaid service plans; advertising &amp; publishing, which included its directory operations that published Yellow and White Pages directories and sold directory and Internet‐based advertising; and other, which included operations from Sterling, its business integration software and services subsidiary, as well as corporate and other operations.

AT&amp;T Inc

AbstractCommunications (MIC: 10.1 SIC: 4813 NAIC: 517110)AT&amp;T is a holding company providing telecommunications services. As of Dec 31 2006, Co. was divided into four reportable segments: wireline, which consisted of three product‐based categories: voice, data and other; wireless, which provided a range of nationwide wireless voice communications services in a variety of pricing plans, including postpaid and prepaid service plans; directory, which included its directory operations that published Yellow and White Pages directories and sold directory and Internet‐based advertising; and other, which included operations from Sterling, its business integration software and services subsidiary, as well as corporate and other operations.

AT&amp;T Inc

AbstractCommunications (MIC: 10.1 SIC: 4813 NAIC: 517110)AT&amp;T is a holding company providing telecommunications services. As of Dec 31 2006, Co. was divided into four reportable segments: wireline, which consisted of three product‐based categories: voice, data and other; wireless, which offered a range of nationwide wireless voice communications services in a variety of pricing plans, including postpaid and prepaid service plans; directory, which included its directory operations that published Yellow and White Pages directories and sold directory and Internet‐based advertising; and other, which included operations from Sterling, its business integration software and services subsidiary, as well as corporate and other operations.

AT&amp;T Inc

AbstractCommunications (MIC: 10.1 SIC: 4813 NAIC: 517110)AT&amp;T is a holding company providing telecommunications services. As of Dec 31 2006, Co. was divided into four reportable segments: wireline, which consisted of three product‐based categories: voice, data and other; wireless, which offered a range of nationwide wireless voice communications services in a variety of pricing plans, including postpaid and prepaid service plans; directory, which included its directory operations that published Yellow and White Pages directories and sold directory and Internet‐based advertising; and other, which included operations from Sterling, its business integration software and services subsidiary, as well as corporate and other operations.

AT&amp;T Inc

AbstractCommunications (MIC: 10.1 SIC: 4813 NAIC: 517110)AT&amp;T is a holding company providing telecommunications services. At Dec 31 2006, Co. was divided into four reportable segments: wireline, which consisted of three product‐based categories: voice, data and other; wireless, which offered a range of nationwide wireless voice communications services in a variety of pricing plans, including postpaid and prepaid service plans; directory, which included its directory operations that published Yellow and White Pages directories and sold directory and Internet‐based advertising; and other, which included operations from Sterling, its business integration software and services subsidiary, as well as corporate and other operations.

The Present and Future of Internet Search

Search engines were crucial in the development of the World Wide Web. Web-based information retrieval progressed from simple word matching to sophisticated algorithms for maximizing the relevance of search results. Statistical and graph-based approaches for indexing and ranking pages, natural language processing techniques for improving query results, and intelligent agents for personalizing the search process all show great promise for enhanced performance. The evolution in search technology was accompanied by growing economic pressures on search engine companies. Unable to sustain long-term viability from advertising revenues, many of the original search engines diversified into portals that farm out their search and directory operations. Vertical portals that serve focused user communities also outsource their search services, and even directory providers began to integrate search engine technologies from outside vendors. This article brings order to the chaos resulting from the variety of search tools being offered under various marketing guises. While growing reliance on a small set of search providers is leading to less diversity among search services, users can expect individualized searching experiences that factor in personal information. The convergence of technology and business models also results in more narrowly defined search spaces, which will lessen the quantity of search results while improving their quality.

A weighted voting algorithm for replicated directories

Weighted voting is used as the basis for a replication technique for directories. This technique affords arbitrarily high data availability as well as high concurrency. Efficient algorithms are presented for all of the standard directory operations. A structural property of the replicated directory that permits the construction of an efficient algorithm for deletion is proven. Simulation results are presented and the system is modeled and analyzed. The analysis agrees well with the simulation, and the space and time performance are shown to be good for all configurations of the system.