Synchronous to semi-synchronous out-of-band i/o

A non-transitory computer readable medium containing software that handles I/O operations between a storage system and a host, the software comprising:

• executable code that initiates synchronous direct data transfers for the I/O operations, the synchronous direct data transfers initially excluding other processes from using a CPU of the host, the synchronous direct data transfers using a first connection between the host and the storage system;
• executable code that sets a first timer for each of the synchronous direct data transfers;
• executable code that transfers data of each of the synchronous direct data transfers that is unsent after the first timer expires using semi-synchronous I/O operations that release the CPU for use by other processes and transfer the data directly via the first connection between the storage system and the host;
• executable code that sets a second timer that corresponds to an expected completion of the semi-synchronous I/O operation;
• and
• executable code that transfers data of each of the semi-synchronous I/O operations that is unsent after the second timer expires using asynchronous I/O operations that transfer the data via a second connection between the storage system and the host, the second connection being separate from the first connection.

A computer system, comprising:

• a processor;
• a controller, coupled to the processor, that communicates with a storage system coupled to the computer system;
• and
• a non-transitory computer readable medium coupled to the processor and to the controller and containing software that handles I/O operations between a storage system and the computer system, the software including executable code that initiates synchronous direct data transfers for the I/O operations, the synchronous direct data transfers initially excluding other processes from using the processor, the synchronous direct data transfers using a first connection between the computer system and the storage system, executable code that sets a first timer for each of the synchronous direct data transfers, executable code that transfers data of each of the synchronous direct data transfers that is unsent after the first timer expires using semi-synchronous I/O operations that release the CPU for use by other processes and transfer the data directly via the first connection between the storage system and the computer system, executable code that sets a second timer that corresponds to an expected completion of the semi-synchronous I/O operation, and executable code that transfers data of each of the semi-synchronous I/O operations that is unsent after the second timer expires using asynchronous I/O operations that transfer the data via a second connection between the storage system and the controller of the computer system, the second connection being separate from the first connection.