I have a question here about Oracle data guard.

After performing a switchover, we shutdown the new standby database and startup it. At this stage, sometimes I find DBA performance in 2 different steps:

  1. startup mount;
  2. startup nomount; then alter database mount standby database;

What's the difference between above commands? Could somebody tell me?

Thanks for helping me and forgive me about my English writing.


2 Answers 2


From the documentation:


The startup_clauses let you mount and open the database so that it is accessible to users.

MOUNT Clause

Use the MOUNT clause to mount the database. Do not use this clause when the database is already mounted.


You can specify MOUNT STANDBY DATABASE to mount a physical standby database. The keywords STANDBY DATABASE are optional, because Oracle Database determines automatically whether the database to be mounted is a primary or standby database. As soon as this statement executes, the standby instance can receive redo data from the primary instance.

startup mount is the same as startup nomount; alter database mount.

So there is no practical difference between the two approaches you showed, if the commands are run consecutively (i.e. you are not doing anything else while it is started but not mounted). However, including STANDBY DATABASE in the command clearly shows intent, so I think it's generally better to include it, particularly if you're scripting this as part of a switchover process.


Startup mount: This command is Useful to bring the database into the mount state.This mode is Useful for recovery of the database. in this mode only dba can access full database.

Startup nomount: This command is Useful for two purpose. 1:To create A New database 2:To create new control file to the existing database

Anyways in your scenario, both approaches are same.

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