In an effort to meet the increasing throughput demands on the SunOS file system made both by applications and higher performance hardware, several optimization paths were examined. The principal constraints were that the on−disk file system format remain the same and that whatever changes were necessary not be user−visible. The solution arrived at was to approximate the behavior of extent based file systems by grouping I/O operations into clusters instead of dealing in individual blocks. A single clustered I/O may take the place of 15−30 block I/Os, resulting in a factor of two increased sequential performance increase. The changes described were restricted to a small portion of the file system code; no user−visible changes were necessary and the on-disk format was not altered.

Version 1 A Guide to Understanding Covert Channel Analysis of Trusted Systems provides a set of good practices related to covert channel analysis. We have written this guide to help the vendor and evaluator communities understand the requirements for covert channel analysis as described in the Department of Defense Trusted Computer System Evaluation Criteria (TCSEC). In an effort to provide guidance, we make recommendations in this technical guide that are not cited in the TCSEC. This guide is the latest in a series of technical guidelines published by the National Computer Security Center. These publications provide insight to the TCSEC requirements for the computer security vendor and technical evaluator. The goals of the Technical Guideline Program are to discuss each feature of the TCSEC in detail and to provide the proper interpretations with specific guidance.

. The buffer cache management algorithm used by almost all operating systems is known as LRU(Least Recently Used). LRU is known to perform well in applications with irregular reference pattern. However, it shows poor performance for sequential-pattern or looping-pattern applications with large-size data. For sequential or looping reference pattern, MRU(Most Recently Used) replacement policy is frequently used to improve the buffer cache performance. On the way of implementing MRU on Linux, we observed that MRU shows lower response time by up to 100% compared to LRU. Indirect blocks, which are used in the file structure of Unix family operating systems for large-size file, are the main reason of decreasing performance. Indirect blocks are fetched but immediately replaced by MRU replacement policy, even those will be soon and frequently needed again. Based on this observation, we propose a buffer replacement policy named `LMRU'. LMRU maintains frequently-used blocks such as indirect bl...

This work is a beginning towards our efforts to build a multi-server emulation of Unix over Mach. In this thesis, we present the design of a file server architecture for emulating Unix file services over Mach. We have chosen to have a separate file server for each type of file system in order to have a modular system structure. The presented design is applicable to all types of file systems. Currently the rest of the services are provided by a thinned down version of the Lites server. An implementation of a server for the fast file system of BSD is also presented. Experiments show that the performance of this server is comparable to that of the original Lites server. Contents 1 Introduction 1 1.1 Microkernels : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 1.2 Unix as an Application Program : : : : : : : : : : : : : : : : : : : : : 3 1.3 Single server vs Multi-server Emulation : : : : : : : : : : : : : : : : : 3 1.4 The Present Work : : : : : : : : : : : : : : : : : ...

In an effort to meet the increasing throughput demands on the SunOS file system made both by applications and higher performance hardware, several optimization paths were examined. The principal constraints were that the on-disk file system format remain the same and that whatever changes were necessary not be user-visible. The solution arrived at was to approximate the behavior of extent based file systems by grouping I/O operations into clusters instead of dealing in individual blocks. A single clustered I/O may take the place of 15-30 block I/Os, resulting in a factor of two increased sequential performance increase. The changes described were restricted to a small portion of the file system code; no user-visible changes were necessary and the on-disk format was not altered. Introduction File systems are a common place to find performance problems. The original UNIX file system [Thompson] is elegant in its simplicity: it has a single block size and a simple list based allo...