Patent ID: 7870093

Claim:
A computer system comprising: a computer; a first storage system, which is coupled to the computer and which receives a write request from the computer; and a second storage system which is coupled to the computer and the first storage system; wherein the first storage system further comprises: a first control unit which processes the write request from the computer; a first storage which stores data related to the write request targeted to the first storage from the computer; a second storage, coupled to the first control unit, which records write data related to the write request targeted to the first storage from the computer with one of time information and sequence number, and a plurality of checkpoints in time for recovery, as log data of the first storage, wherein the checkpoints identify a system state at detections of certain types of transactions, wherein the second storage system further comprises: a second control unit which processes data from the computer and/or the first storage system; a third storage which stores data related to the transferred data targeted to the third storage from the first storage system; and a fourth storage, coupled to the second control unit, which records data from the computer with one of time information and sequence number, and a plurality of checkpoints in time for recovery, as log data of the third storage, wherein the checkpoints identify a system state at detections of certain types of transactions.