Hi Pedro,
If you are now using COMP-3 instead of COMP-6 then your fields will be larger. COMP-6 in RM is unsigned PACKED-DECIMAL and COMP-3 in VC is signed PACKED-DECIMAL so an extra byte of storage may be required to hold the sign.
You can emulate the RM COMP-6 behavior by using the RM dialect directive which will set the COMP-6"2" directive on. Then if you define your data as COMP-6 and it has no sign in the PIC then the extra byte will not be used.
You can also specify data and key compression on your files using the DATACOMPRESS or KEYCOMPRESS directives or by setting this on in a file handler configuration file.
Thanks