This article describes what is contained in the Subsystem Analyzer FMT_WIO column.
What is contained in the Subsystem Analyzer FMT_WIO column?
z/OS 1.11 and above.
This column contains a count of the DB2 pre-formatting I/O's of new pages in a table space during execution time.
A common reason would be Inserts which cause new extents to be built and new pages to be formatted by DB2.
If the PREFORMAT option is used in a LOAD or REORG utility, depending upon the size of the object, this could generate a substantial amount of "Format Write I/O's".