Patent ID: 8977896
Filing Date: 2015-03-10
Classification: G06F

Abstract:
1. A method of managing state transitions in a data migration operation, the migration operation including an initial setup state, a set of write cloning states in which a target storage device is becoming or is maintained synchronized with a source storage device, and a later committed state in which the target storage device is used to the exclusion of the source storage device, the set of write cloning states spanning a system shutdown/startup cycle, comprising: upon entering the write cloning states, setting an error flag used to protect against data corruption in the event of a non-clean system shutdown; during the write cloning states, performing only allowed state transitions based on recorded device faults, the allowed state transitions including a non-error transition to the committed state when no device fault is recorded for the target storage device and an error transition to the setup state when a device fault is recorded for the target storage device; in the event of a clean system shutdown, completing a shutdown procedure in which a device fault detected during writing to the target storage device is recorded and the error flag is cleared, the recording of the device fault forcing the error transition of the migration operation during subsequent operation after system startup; and during the system startup prior to enabling application input/output to the target storage device, determining whether the error flag is set indicating that the shutdown procedure was not completed, and only if the error flag is set then recording a device fault for the target storage device to force the error transition of the migration operation during subsequent operation.