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Experiments with Automatic File Migration Disclosure Number: IPCOM000131515D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Nov-11
Document File: 9 page(s) / 36K

Publishing Venue

Software Patent Institute

Related People

D. H. Lawrie: AUTHOR [+5]


Virtual memory techniques can be used effectively to study file migration policies. An extensive data base of file access patterns allows simulation of policy performance.

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Experiments with Automatic File Migration

D. H. Lawrie, J. M. Randal, and R. R. Barton

University of Illinois

Virtual memory techniques can be used effectively to study file migration policies. An extensive data base of file access patterns allows simulation of policy performance.

The use of magnetic tape for file storage is tolerable in many batch-oriented systems where the time required to mount a tape is not particularly significant. Recently we have seen considerable growth in the use of timesharing systems and, at the same time, in the need for on-line file storage. Timesharing users require much faster access to their files, and this has led to a marked increase in the use of disk storage devices for file storage. Too often the problem of managing these files has been left to the user. Given a finite amount of on-line file storage space, users must decide which files should be moved to archival storage, which should be purged, and so on. Frequently they must also produce backup copies of their files to protect against potential disk catastrophies.

Research into virtual memory systems is certainly not new and traditionally has involved collection and analysis of address traces from real programs. With such traces, one can easily determine the time between page faults, given fixed or dynamic amounts of primary memory and specific page- replacement algorithms. It is well known that programs exhibit a characteristic called "locality," which means that memory references are not uniformly distributed throughout the address space, but instead tend to remain in fixed localities for periods of time. Thus, we need to keep only these localities or "working' sets" of accesses in primary memory.

We have taken a similar approach to the study of file accesses. By collecting copies of the disk file catalogs on a daily basis over a period of several years, we have determined to what extent locality principles exist in file access patterns and to what extent these patterns may be useful in managing user files.

Smith ~ has done a very thorough and interesting analysis of file size and activity patterns. Many of his findins~c ~ ret v~rv cimil ~ r tr, `~ 'rc even t her oh ~' r in at :a ll :atirmc

are quite different and even though the purposes of the files in the study are different. For example, Smith was constrained to sample Wylbur data sets and excluded tape and certain system files. Our sample includes all data sets cataloged under the Control Data NOS operating system. This includes small procedure files, and very large...