AN OPTIMAL l / N BACKUP POLICY FOR DATA FLOPPY DISKS UNDER EFFICIENCY BASIS

A word processor has become one of essential devices used in offices. Document files created by using a word processor are generally preserved on a floppy disk 01' floppy disks for referencE's. Nevertheless, the files stored on a floppy disk art' occasionally lost due to human errors. the life of the floppy disk and a failure of hardware devices, which comprise the word processor. This is callpd a floppy disk failure. One of the simplest methods for protecting us from such serious losses is to hackup files on anotlwf floppy disk. Frequent. backup operations would spend much time in themselves although they could reduce the loss at a floppy disk failure. On the contrary, occasional backup operations would make the loss at a floppy disk failure very large although they could save time in backup operat.ions. These observations reveal the significance of determining an adequate backup timing of files. The present study proposes a 1/ N backup policy for data floppy disks. which suggests to backup files when 1/ N of the total memory of a floppy disk is consumed. The availability of the proposed backup policy is formulated as an objective function under efficiency basis. The ('xistene(' of an optimal integer N* that maximizes the availabilit.y is then examined to clarify the condit.ions uncleI' which sHch an optimal integer exists. Numerical examples are also presented.