RETRY METHOD AND APPARATUS FOR USE IN A MAGNETIC RECORDING AND REPRODUCING SYSTEM

摘要

A magnetic tape subsystem includes a peripheral controller which processes data signals of a block received during the reading and recording of the block on a magnetic tape medium by a selected one of a plurality of magnetic tape devices in response to commands received from a data processing system. The peripheral controller includes a data recovery unit having a plurality of storage indicators. These indicators are set by the controller in accordance with the characteristics of the block of data signals recovered by the data recovery unit providing indications of the results of the reading or recording operation performed by the selected magnetic tape device during the peripheral controller's execution of the command. The controller divides up the interval of time of an operation into a number of time periods and monitors the characteristics of the signals of a block which should be received by the data recovery unit during those intervals. During execution of a write command, the controller monitors the tape recording or write operation during different time intervals by monitoring the continuity of the signals recorded by the magnetic tape device indications of which the data recovery unit receives during its performance of a read after write checking operation. The various indicators signal whether the block written was normal or was damaged in addition to signaling the extent of damage which occurred during the writing of the block. Signals representative of the indications are grouped to specify at least two types of error conditions which are tested by the controller to establish whether the command is retryable and nonretryable. The peripheral controller initiates a retry of the command executed only when the indicators signal that the extent of damage has not exceeded a predetermined amount thereby ensuring that only commands which can be retried successfully are re-executed. The controller performs similar monitoring operations during the execution of read commands for establishing signal indications used in determining whether the command should be retried upon detection of errors in the block read by the data recovery unit.