What is cut-through switching?
Cut-through switching is a switching method used in packet switching systems in which the switch forwards packets or frames to their destination immediately after processing the destination address without waiting for all the data to be received.
The switch immediately transmits packets it receives and uses CRC checks to check for errors, and then relies on the target devices to troubleshoot the transmitted corrupted data that it has flagged. In this case, the switch can be viewed as a pure forwarder of data packets and therefore offers performance with low latency.
Cut-through switching provides low latency for SCSI traffic and is primarily used in fiber channels. Cut-through switches perform cyclical redundancy checks on incoming packets and mark the damaged frame EOF field as invalid. The target devices see the invalid flag and delete the frame before it reaches the application. This is a reliable error handling method that minimizes the time it takes to recover bad frames because the recovery starts immediately compared to the 'Store and Forward' method which forces a SCSI timeout at the point where the bad frame is detected can. SCSI retry to restore would take an additional few seconds of waiting.
Cut-through switching is primarily used in Fiber Channel because the reliability of target-based error handling is dictated by the standards of the Technical Committee T11, which impose Fiber Channel standards.