Method and apparatus for executing critical disk access commands

Abstract

The present invention is a controller and a method for its use in a disk data storage and retrieval system. The controller is of the type which associates a file mask with a sequence of commands. The controller has means for executing a critical-section-start (CSS) command received from the host computer which indicates to the controller that a critical sequence of commands will follow and places the controller in a critical sequence mode (CS mode). The controller has means for executing a critical-section-end (CSE) command which indicates the end of the commands. While in the CS mode the controller checks the file mask for each command received and refuses to execute selected commands which are not associated with predetermined values of the file mask (CS file masks). A program running on the host computer sends the controller a command establishing a CS file mask and the CSS command, then the program sends one or more sequences of critical commands to the controller. After the critical commands have completed successfully, the program sends the CSE command which returns the controller to the normal operating mode. If the critical commands fail then appropriate error recovery is performed while the controller is in the CS mode. The CS mode is used in conjunction with CS file masks to effect limitation of access to the disk system while critical commands are executing. More particularly the controller is used to perform concurrent media maintenance wherein media maintenance is performed on a suspect track while the user data formerly on that track is fully accessible by virtue of being copied to an alternate track.