An efficient backup warning policy for a hard disk

In this decade, a hard disk has become an essential key component of a personal computer system. It preserves important information which is frequently updated. In case the hard disk fails, we may possibly lose such important information. This is called a hard disk failure. One of the simplest methods for coping with such a possibility of a hard disk failure is to periodically make a copy of the information to another secondary medium. This is called a backup operation. This study discusses an efficient backup warning policy which gives us a warning to back up files at the prespecified time Tw measured by the elapsed time since the previous backup operation or the recovery from a hard disk failure, whichever occurs first. For the purpose of determining the value of Tw, this study formulates the efficiency as a criterion, which is defined by the long-run average ratio of 1. (i) the time spent in processing jobs effectively in the sense that their accomplishments are successfully backed up, to2. (ii) the total time spent in processing jobs ineffectively as well as effectively, and spent in backup or recovery operations. We then clarify the conditions under which an optimal warning time exists. A numerical example is also presented.