Reading the recs is only one aspect of the problem. How do you plan to process them once you've read them? Do you have a copybook or record layout? Are the records you're reading have predetermined record lenths? For example is one type of rec 123 bytes; anothe type 42 bytes, etc. Or can the records vary in length because they contain a table that can vary in length from rec to rec.
Do you plan to write them to another file?
If you can answer some of these questions we may be able to pose a solution.