Synchronous input/output command

A computer program product, the computer program product comprising a computer readable storage medium having program instructions for performing synchronous input/output (I/O) operations embodied therewith, the program instructions executable by a processor to cause the processor to perform:

• sending, from an operating system (OS) executing on a server to firmware located on the server, a request to perform a unit of work that includes a synchronous I/O operation, the request comprising a command request block that includes an identifier of a persistent storage control unit (SCU);
• waiting, by the OS, for the synchronous I/O to complete, wherein the unit of work remains active during the waiting;
• detecting, by the firmware, that the synchronous I/O operation has completed;
• receiving, by the OS, a command response block from the firmware that includes completion status information about the synchronous I/O operation;
• and
• completing the unit of work in response to the I/O operation completing,
• wherein the command request block further includes an incremented sequence number that provides the SCU with an offset of a status area within the firmware for the command response block and a confirmation that a previous command having a sequence number prior to the incremented sequence number has been completed.