ORACLE- Database unable to START/OPEN When I'm trying to start a database (after a server patch was applied), I get the following error and I am unable to open the database.

SQL&gt; startup;
ORACLE instance started.

Total System Global Area 7465926656 bytes
Fixed Size                  2267744 bytes
Variable Size            1241515424 bytes
Database Buffers         6207569920 bytes
Redo Buffers               14573568 bytes
Database mounted.
ORA-10458: standby database requires recovery
ORA-01196: file 1 is inconsistent due to a failed media recovery session
ORA-01110: data file 1:
'/u00/oracle/app/oracle/product/oradata/XRO/sy_XRO.dbf


NOTE: 

SQL&gt; select database_role from v$database;

DATABASE_ROLE
------------------------------------------------
PHYSICAL STANDBY

SQL&gt; select status from v$instance;

STATUS
------------------------------------
MOUNTED
Generally you can open standby databases as read only. Specifically you can open data guard standby databases as read only. Did you check to see if all of the data files exist? That a database is mounted, means that the control files are where they are supposed to be, not corrupted and your init/spfile is valid. 

Did you patch the Oracle Home for the standby database with the same patch as the parent? Can you force database recovery on the child to get the databases in sync.