Six bytes and six characters may or may not be equivalent when dealing with multi-byte charactersets. Don't know Exadata but Oracle does both "byte" and "character" semantics. Meaning, if you define a field as VARCHAR(6) BYTES then it won't hold your six characters because... seven bytes. VARCHAR(6) CHAR would hold them since it holds six characters not restricted by byte count. And for some reason, BYTE is the default in Oracle. Been bit in the butt before over that.
Something to look into.