Confusion about recovery of controlfile without backup

[indrajit2002]

Hi,
After creating a controlfile manually without any backup how the database goes to a consistent state? Because the newly created controlfile does not have the scn details as well as checkpoint information that the deleted controlfile had.
Also after restoring the controlfile is it needed to open the database in resetlogs mode? If not why?

Please help me to clear these confusions.

[PaulH]

In a disaster situation where all files are lost you can only recover to the
last SCN in the archived redo logs. Beyond this point the recovery would have to make reference to the online redo logs which are not present.

Disaster recovery is therefore a type of incomplete recovery.

To perform disaster recovery connect to RMAN:

rman catalog=rman/rman@GOLD_CAT target=sys/sysd@GOLD_AUX

startup nomount;
restore controlfile;
alter database mount;


From SQL*Plus as SYS get the last archived SCN using:

Make sure ORACLE_SID is set to DB that needs to be recovered.

sqlplus / AS sysdba


SQL> SELECT archivelog_change#-1 FROM v$database;

ARCHIVELOG_CHANGE#-1
--------------------
1048438

1 row selected.

Back in RMAN do the following:

run {
set until scn 1048438;
restore database;
recover database;
alter database open resetlogs;
}


If the "until scn" were not set the following type of error would be produced once a redo log was referenced:

There is a lesson here always backup up your control files and make sure they
are placed on different disks. If one disk goes bad, you can copy a control
file back into place once the disk is repaired therefore avoiding the restore
of the control files.

Good Luck