Your installation can place all TSO logon information in the RACF® database, thus eliminating the SYS1.UADS data set. However, if your installation deletes SYS1.UADS entirely, and later deactivates RACF with RVARY or at IPL time, no user can log on to the system. To avoid this possibility, your installation should keep at least one user ID (with known password) in the SYS1.UADS data set. This topic is further discussed in Sysplex recovery scenarios that require XCF-local mode.