Associating RACF® user IDs and groups to UIDs and GIDs has important performance considerations. Both the UNIXMAP class and virtual lookaside facility (VLF) should remain active and the VLF classes IRRUMAP and IRRGMAP should be defined to VLF. To understand how VLF can affect performance, refer to the following RACF documentation:

• The section on mapping UIDs to user IDs and GIDs to group IDs in z/OS Security Server RACF System Programmer's Guide.
• The section on using UNIXMAP and VLF in z/OS Security Server RACF Security Administrator's Guide.