Most operating systems use interface interrupts to schedule network tasks. Interrupt-driven systems can provide low overhead and good latency at low of-fered load, but degrade significantly at higher arrival rates unless care is taken to prevent several pathologies. These are various forms of receive livelock, in which the system spends all its time processing interrupts, to the exclusion of other neces-sary tasks. Under extreme conditions, no packets are delivered to the user application or the output of the system. To avoid livelock and related problems, an operat-ing system must schedule network interrupt handling as carefully as it schedules process execution. We modified an interrupt-driven networking implemen-tation to do so; this eliminates receive livelock without degrading other aspects of system performance. We present measurements demonstrating the success of our approach. 1.

The object-based storage model, in which files are made up of one or more data objects stored on self-contained Object-Based Storage Devices (OSDs), is emerging as an architecture for distributed storage systems. The workload presented to the OSDs will be quite different from that of generalpurpose file systems, yet many distributed file systems employ general-purpose file systems as their underlying file system. We present OBFS, a small and highly efficient file system designed for use in OSDs. Our experiments show that our user-level implementation of OBFS outperforms Linux Ext2 and Ext3 by a factor of two or three, and while OBFS is 1/25 the size of XFS, it provides only slightly lower read performance and 10%--40% higher write performance.

In this paper we introduce DualFS, a new high performance journaling file system that puts data and meta-data on different devices (usually, two partitions on the same disk or on different disks), and manages them in very different ways. Unlike other journaling file systems, DualFS has only one copy of every meta-data block. This copy is in the metadata device, a log which is used by DualFS both to read and to write meta-data blocks. By avoiding a time-expensive extra copy of meta-data blocks, DualFS can achieve a good performance as compared to other journaling file systems. Indeed, we have implemented a DualFS prototype, which has been evaluated with microbenchmarks and macrobenchmarks, and we have found that DualFS greatly reduces the total I/O time taken by the file system in most cases (up to 97%), whereas it slightly increases the total I/O time only in a few and limited cases.

File system consistency frequently involves a choice between raw performance and integrity guarantees. A few software-based solutions for this problem have appeared and are currently being used on some commercial operating systems; these include log-structured file systems, journaling file systems, and soft updates. In this paper, we propose meta-data snapshotting as a low-cost, scalable, and simple mechanism that provides file system integrity. It allows the safe use of write-back caching by making successive snapshots of the meta-data using copy-onwrite, and atomically committing the snapshot to stable storage without interrupting file system availability. In the presence of system failures, no file system checker or any other operation is necessary to mount the file system, therefore it greatly improves system availability. This paper describes meta-data snapshotting, and its incorporation into a file system available for the Linux and K42 operating systems. We show that metadata snapshotting has low overhead: for a microbenchmark, and two macrobenchmarks, the measured overhead is of at most 4%, when compared to a completely asynchronous file system, with no consistency guarantees. Our experiments also show that it induces less overhead then a write-ahead journaling file system, and it scales much better when the number of clients and file system operations grows.

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Unix’s lack of a robust and expandable file system has become a significant problem with the growth of UNIX in large commercial environments. The HAMFS (Highly Available Multi-server File System) is a cluster file system designed to address this need. HAMFS offers disk-pooling, supports off-the-shelf disks, and automatically balances file load across disks dynamically. Data residing in a disk pool is directly accessible from every node in a HAMFS cluster. As user’s capacity requirements grow, HAMFS provides easy disk pool expansion. Finally, HAMFS provides uniform scaling of file system performance from a single node configuration to large multi-node clusters, offering significant performance advantage over traditional file systems. For example, in short file access situations, HAMFS provide a factor of five performance improvement over NFS, and a factor of two improvement over conventional local file systems. Technologies developed for HAMFS are applied to Fujitsu’s file system product SafeFILE. 1.

The UNIX Fast File System (FFS) is probably the most widely-used file system for performance comparisons. However, such comparisons frequently overlook many of the performance enhancements that have been added over the past decade. In this paper, we explore the two most commonly used approaches for improving the performance of meta-data operations and recovery: logging and Soft Updates.

: In most modern local area network environments, NFS is used to provide remote file storage on a particular server machine. A consequence of this distributed architecture is that the failure of the server results in paralysis or a loss of work for users. This paper presents the design of a low-cost fault tolerant NFS server which can be installed on most Unix networking environments. FT-NFS runs as a user process and does not necessitate any underlying specific operating system functionality. The originality of our approach relies on the use of a stable cache which provides data availability and resiliency to a single failure. The main benefits of the stable cache are first to allow disk write operations to be safely performed in the background and second to permit the gathering of small files in large containers. The latter technique permits disk I/Os to be improved by reducing their number and increasing their length. Under the nhfsstone benchmark, FT-NFS outperforms the in-kernel S...

This thesis discusses the design and implementation of dtfs, a log-structured filesystem for Linux. dtfs features a generic core providing logging facilities that are filesystem-independent and a "filesystem personality" that borrows heavily from the Linux ext2 filesystem. Furthermore, the dtfs design supports the placement of multiple filesystems (even of different filesystem personalities) on top of one dtfs filesystem device and the creation of snapshots and different versions for these filesystems.

A Systematic Characterization of Application Sensitivity to Network Performance by Richard Paul Martin Doctor of Philosophy in Computer Science University of California at Berkeley Professor David E. Culler, Chair This thesis provides a systematic study of application sensitivity to network performance. Our aim is to investigate the impact of communication performance on real applications. Using the LogGP model as an abstract framework, we set out to understand which aspects of communication performance are most important. The focus of our investigation thus centers on a quantification of the sensitivityof applications to the parameters of the LogGP model: network latency, software overhead, per-message and per-byte bandwidth. We define sensitivity as the change in some application performance metric, such as run time or updates per second, as a function of the LogGP parameters. The strong association of the LogGP model with real machine components allows us to draw architectural conclusions from the measured sensitivity curves as well.