An ASM instance has a few other unique characteristics. Although it does have an initialization
parameter file and a password file, it has no data dictionary, and therefore all connections to an
ASM instance are via SYS and SYSTEM using operating system authentication only; you can only
connect to an ASM instance with the connect / as sysdba command; any username/password in
the connect command is ignored. Disk group commands such as create diskgroup, alter diskgroup,
and drop diskgroup are only valid in an ASM instance. Finally, an ASM instance is either in a
NOMOUNT or MOUNT state; it is never in an OPEN state.
ASM Instance Components
ASM instances cannot be accessed using the variety of methods available with a traditional
database. In this section, I??™ll talk about the privileges available to you that connect with SYSDBA
and SYSOPER privileges. We??™ll also distinguish an ASM instance by the new and expanded
initialization parameters (introduced in Oracle Database 10g and enhanced in Oracle Database
11g) available only for an ASM instance. At the end of this section, I??™ll present the procedures for
starting and stopping an ASM instance along with the dependencies between ASM instances and
the database instances they serve.
Accessing an ASM Instance
As mentioned earlier in the chapter, an ASM instance does not have a data dictionary, so access
to the instance is restricted to users who can authenticate with the operating system??”in other
words, connecting as SYSDBA or SYSOPER by an operating system user in the dba group.
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