File Control Bytes/sec is the overall rate at which bytes are transferred for all file system operations that are neither ...

File Control Bytes/sec is the overall rate at which bytes are transferred for all file system operations that are neither reads nor writes, including file system control requests and requests for information about device characteristics or status.  It is measured in numbers of bytes.  This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval.