Method and apparatus for efficient updating of ckd data stored on fixed

Abstract

A method and apparatus for updating CKD data stored on fixed block media, and more particularly to creating Track Format Descriptors which are data structures loaded into electronic memory to enable fast writing of data without loading an entire CKD emulated track of data into memory. A control unit is provided with logic to provide Track Format Descriptors which describe the format of the track without the need for the data content of the track to be resident in cache, or electronic memory. An emulated CKD volume corresponds to a volume of data stored on a multi-disk device. Each track on a volume is represented by a Track Format Descriptor. The Track Format Descriptor forms a representation of the format according to the following general procedure. If the format is a predefined format, in other words one that is already known by the control unit then a track form descriptor is formed to represent the format. If the format is easily discernible, it is said to be 'well behaved'. 'Well behaved' formats are ones in which either each record has the same field length, there is no key field, or record numbers start at one and increment by one. A Track Format Descriptor is formed by predicting the format of these so called 'well behaved' formats. If the format is not 'well behaved' and the format has not been predefined, then the entire data track must be loaded into cache memory, before a fast write operation is performed. The Track Format Descriptor serves as an index to other information data structures which are loaded into memory when required by logic in the control unit.