Example implementations relate to determining lengths of acknowledgment delays for input/output (I/O) commands. In example implementations, a length of an acknowledgment delay for a respective I/O command may be based on cache availability, and activity level of a drive at which the respective I/O command is directed, after the respective I/O command has been executed. Acknowledgments for respective I/O commands may be transmitted after respective periods of time equal to respective lengths of acknowledgment delays have elapsed.