Because you obtain the most benefit from LLA when you have both LLA and VLF functioning, you should plan to use both. When used with VLF, LLA reduces the I/O required to fetch modules from DASD by causing selected modules to be staged in VLF data spaces. LLA does not use VLF to manage library directories. When used without VLF, LLA eliminates only the I/O the system would use in searching library directories on DASD.