ORA-01105: mount is incompatible with mounts by other instances

 If you face ORA-01105 while starting an Oracle instance in a RAC environment, it means that there is a parameter in init file (of spfile) that is required to have an identical value across all RAC instances. But, the parameter is set differently in the init file of current instance that you are trying to start.

ORA-1105 signalled during: ALTER DATABASE

Alert log would report error similar to the specified above. Snippet from the alert log could be similar to the following

… … … SUCCESS: diskgroup DATA was mounted SUCCESS: diskgroup REDO1 was mounted SUCCESS: diskgroup REDO2 was mounted Tue May 01 14:50:07 2018 NOTE: dependency between database PROD and diskgroup resource ora.DATA.dg is established NOTE: dependency between database PROD and diskgroup resource ora.REDO1.dg is established NOTE: dependency between database PROD and diskgroup resource ora.REDO2.dg is established ORA-1105 signalled during: ALTER DATABASE   MOUNT... Tue May 01 14:50:16 2018 SUCCESS: diskgroup REDO2 was dismounted SUCCESS: diskgroup REDO1 was dismounted SUCCESS: diskgroup DATA was dismounted Tue May 01 14:53:13 2018 NOTE: ASMB process exiting due to lack of ASM file activity for 183 seconds Stopping background process RBAL Stopping background process MARK Tue May 01 14:53:15 2018 NOTE: Shutting down MARK background process Tue May 01 14:54:50 2018 Shutting down instance (immediate) Shutting down instance: further logons disabled Stopping background process MMNL Stopping background process MMON License high water mark = 7 All dispatchers and shared servers shutdown ALTER DATABASE CLOSE NORMAL ORA-1507 signalled during: ALTER DATABASE CLOSE NORMAL... ARCH: Archival disabled due to shutdown: 1089 Shutting down archive processes Archiving is disabled ARCH: Archival disabled due to shutdown: 1089

ORA-19808: recovery destination parameter mismatch

In my case, ORA-19808 was accompanied by ORA-01105.

SQL> startup mount ORACLE instance started.   Total System Global Area 5.8792E+10 bytes Fixed Size                  2269424 bytes Variable Size            6979325712 bytes Database Buffers         5.1674E+10 bytes Redo Buffers              136728576 bytes ORA-01105: mount is incompatible with mounts by other instances ORA-19808: recovery destination parameter mismatch

 The reason of this error was that my db_recovery_file_dest_size parameter on current instance was not same as other 2 instances. Instance 2 and 3 had this value set to 500G whereas on instance 1 it was set to 800G. After starting instance 1 in nomount, following query showed the value of db_recovery_file_dest_size on all instances

SQL> select inst_id,value from gv$parameter where name='db_recovery_file_dest_size';    INST_ID                                  VALUE ------------------------------------------------------------------------------------------          3                                       536870912000          2                                       536870912000          1                                       858993459200

After I set the value of db_recovery_file_dest_size to 500G for the instance 1, I was able to successfully start the instance 1.