VSAM KSDS datasets require either 7 or 10 bytes of overhead at the end of each CI for control purposes. Also, VSAM permits KSDS data sets to be defined (DEFINE) by using the FSPC=(%CI,%CA) to accommodate future inserts. However, VSAM will not permit ESDS data sets to be defined by using with the FSPC=(%CI,%CA) parameter. Instead, IMS can be told to accommodate future inserts through the use of the FRSPC= (FBFF, FSPF) parameter being coded as a parameter on the DATASET macro.