Disk volume data storage and recovery method

Abstract

In a word processing system, a text stream is stored on a direct access storage device (DASD) for recall and editing. The text stream is organized into a document that is stored on the DASD as a data set. The data set comprises an index portion and a portion containing text records. The index portion is divided into nodes, of which the primary node is called the root node. A method called shadowing is introduced to protect index nodes from the loss of significant data. Status indicators are defined and maintained so that access to a data set for normal system operation may be prevented where there is significant chance that the data set index has errors or is inconsistent to the extent that the normal high performance access method routines may not be able to use the index or may cause inadvertent loss of valid text data. Recovery mechanisms enable all of the data on the DASD which can be located by indexes to be restored after normal terminations during complex data set index updates or when intermediate nodes in large data sets are lost due to storage media input physical errors.