Multiprocessor system for updating status information through flip-flopping read version and write version of checkpoint data

摘要

An apparatus and method employs dual checkpoint data sets for communicating system status. A journal of changed data is implemented to reduce I/O to a subsystem's shared data area on a non-volatile shared storage device. The journal provides for an increase in the amount of time that a processor may have access to the shared data area. Also, two versions of the data area are implemented in order to insure the integrity of the continuously updated data area. The two versions flip-flop depending upon which one has the most recent updates. That is, the version that has the most recent updates becomes the to-be-read-from data area and is read by the processor that currently has access to the shared data area during this series of I/O operations. The other version becomes the to-be-written-to data area and is written to by the processor that currently has access to the data area in order to update the to-be-written-to version to the current level. The to-be-written-to version then becomes the to-be-read-from version during the next series of I/O operations.