ORA-00202: controlfile: ‘C:\ORACLE\ORADATA\ORACLE91\CONTROL02.CTL’
ORA-27091: skgfqio: unable to queue I/O
ORA-27070: skgfdisp: async read/write failed
OSD-04006: ReadFile() failure, unable to read from file
O/S-Error: (OS 23) Data error (cyclic redundancy check).
i find this problem on one of my server database. this problem will make oracle fail to mount and open. if you try to connect via sqlplus, you will get error message : Oracle is on initialization startup/shutdown. so you can not enter the database.
below is the step that i do, to resolve the problem.(oracle ver 9i and higher)
1. connect to database using sqlplus with SYS as SYSDBA
2. shutdown immediate the database.
3. create a backup copy of all control file(usually consist of 3 control file with extension CTL) on folder ORADATA\
4. rename CONTROL02.CTL (corrupt control file) to CONTROL02.bak
5. rename one of working control file to become CONTROL02.CTL and then copy this file to folder ORADATA\
6.then startup the database via sqlplus using SYS as SYSDBA
this step only working if one of controlfile is corrupt and need to be replace. and also your controlfile is multiplex. Make sure that the error message is exactly the same with what is written above.