I/O control, synchronization method in a raid environment with co-existing hardware and software-based I/O paths

The present invention is directed to a command block protocol which may implemented by RAID firmware for synchronizing I/Os in a RAID system which includes co-existing hardware and software-based I/O paths. The command block protocol of the present disclosure ensures that there aren't any I/Os outstanding in the fast path or any other hardware engine by making sure that the region lock (ex.-Sentinel Region Lock) is taken for the entire size of the volume. When the Sentinel Region Lock is granted, the RAID firmware may assume that there aren't any commands outstanding in the fast path hardware or pending for the region lock to be obtained. The RAID firmware would not be able to maintain integrity of user data in the absence of the new command block protocol disclosed herein.