The present invention relates to an information managing apparatus for providing an external apparatus with requested information in response to an instruction from the external apparatus and/or recording information onto a given recording medium.
Recording media used in a computer system include magnetic disks (a hard disk, a flexible disk, and the like) and a magnetic tape. And information managing apparatuses are known which are equipped with a plurality of drive units for such recording media and are capable of managing information by recording and/or reproducing a large amount of information.
For example, in an apparatus using magnetic tapes as recording media (hereinafter referred to as "tape library apparatus"), a number of tape cassettes each incorporating a magnetic tape are accommodated in a prescribed accommodation rack. A desired one of the tape cassettes is taken out by a transfer mechanism and then mounted in a selected one of a plurality of tape drive units. Data recording/reproduction is then performed.
A control means in the tape library apparatus exchanges information with an external apparatus such as a host computer. The tape library apparatus manages information such that it provides the external apparatus with requested information in response to an instruction from the external apparatus by reproducing that information from a magnetic tape through a tape drive unit, or it records information onto a magnetic tape.
Incidentally, in the above type of information managing apparatus, the supply of power to the entire system including a host computer and a tape library apparatus needs to be stopped during replacement of a tape drive unit. That is, at the occurrence of some trouble in the system, in a periodical maintenance/inspection operation, or in like events, it is necessary to remove a tape drive unit from the apparatus or replace a tape drive unit. In such a case, the main power needs to be turned off to stop the system.
However, such a system stop is unfavorable to users. Where a tape library apparatus operates as a data server in a large-scale system, a system down possibly causes serious damage. Therefore, a stop of power supply to the system is not permitted or should be avoided by taking any measures available. It is desired that replacement or the like of a tape drive unit be conducted with the power supply to the system continued, i.e., with the apparatus kept online.
However, if a drive unit is replaced without opening a transmission path between the apparatus and the external apparatus, there is a possibility that electrically adverse effects occur in the drive unit or the transmission path (a bus, for instance), resulting in damage of the drive unit, occurrence of a data error due to introduction of noise, unstable behavior of the system, and other problems.