Digital Equipment Corporation

Peter Stoppani, Jr

Christian D Saether

A computer file system, having a multiplicity of distinct disk storage devices, includes a multiplicity of file directories, stored on various disks. Each file directory is used to translate file names into corresponding tag values. For each disk there is a file descriptor table with a file descriptor entry for every file stored on the disk. A single tag directory contains one tag entry for every file stored in the system. The tag directory is used by the file system to find a file by translating a tag value into a pointer to the disk on which the file is stored and a pointer to the file's file descriptor entry. To move a file from a first disk to a second disk, the file is copied to the second disk, a new file descriptor entry for the copied file is generated in the file descriptor table for the second disk, the copy of the file on the first disk is de-allocated, and the tag entry for the file is updated to point to the second disk and to the file's new file descriptor entry. Thus, a file can be moved from a first disk a second without having to locate and update all the corresponding file directory entries. In a preferred embodiment, the file system includes a routine that monitors disk loading and unused disk capacity. It determines when disk usage is imbalanced and automatically moves files among the disks so as to better balance disk usage.

System of device independent file directories using a tag between the

A computer file system, for use with a computer system having a multiplicity of distinct data storage devices, includes a management program that defines a set of service attributes which characterize operational characteristics of data storage devices. A service class table stores data denoting which of service attributes characterize each distinct storage device. The management program adds data to the service class table when additional data storage devices are added to the computer system. A storage device selection program responds to file allocation requests, which specify a set of service attributes, by comparing the specified set of service attributes with the data stored in the service class table and selecting one of the data storage devices in accordance with predefined service attribute matching criteria. The service attributes used by the file system may include required service attributes and optional service attributes. In that case, the predefined service attribute matching criteria include criteria requiring that the required service attributes of the selected data storage device, as denoted in the service class table, match all required service attributes specified in the corresponding file allocation request. In addition, there are predefined criteria for maximizing matching of specified optional service attributes with the optional service attributes of the selected data storage device.

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Woodinville, WA, United States of America

Peter Stoppani, Jr