Patent ID: 7590809
Filing Date: 2009-09-15
Classification: G06F

Abstract:
1. A computer system, comprising: a first storage system that is coupled to a first host computer; a second storage system that is coupled to a second host computer and the first storage system; and a third storage system that is coupled to the first storage system and the second storage system, wherein: the first storage systems: stores data sent from the first host computer, transfers the data sent from the first host computer to the second storage system by synchronous remote copy, and transfers the data sent from the first host computer to the third storage system by asynchronous remote copy; and the second storage system: comprises a first difference bitmap, updates a bit of the first difference bitmap corresponding to an area to which the data has been written from the second host computer after data is written from the second host computer to the second storage system, transfers the data stored in the area corresponding to the updated bit of the first difference bitmap to the third storage system, instructs the third storage system to delete a pair relationship between the third storage system and the first storage system in response to detecting a failure of the first storage system, monitors a journal transfer between the first storage system and the third storage system to determine that the pair relationship between the first storage system and the third storage system is deleted, creates a third difference bitmap used in connection with asynchronous transfers from the second storage system to the third storage system when it is determined that the pair relationship between the first storage system and the third storage system is deleted, copies bit values of the first difference bitmap to the third difference bitmap, and transfers data from the second storage system to the third storage system based upon the bit values of the third difference bitmap.