Patent ID: 7111139

Claim:
A storage system comprising a plurality of storage subsystems, wherein the plurality of storage subsystems each include a memory and a storage medium for storing data, wherein the plurality of storage subsystems include at least one first storage subsystem and at least one second storage subsystem, the first storage subsystem being connected to the second storage subsystem which is configured to receive and store one or more blocks of data from the first storage subsystem, the first storage subsystem being a preceding storage subsystem to the second storage subsystem, the second storage subsystem being a succeeding storage subsystem to the first storage subsystem; wherein each block of data being copied has an associated sequence number in ascending order, wherein the memory in each of the storage subsystems includes a queue to receive and store the one or more blocks of data and a sequence number associated with each block of data, a last sequence number record to store a last sequence number associated with a last block of data received by the queue, and a table to store a last sequence number received from each succeeding storage system connected to the storage subsystem, wherein each storage subsystem includes a processor configured to search the smallest last sequence number in the table.