You have backed up your database using image copies. You have lost the SYSTEM
tablespace and need to restart your database as quickly as possible. What is the correct
solution?
A.
Restore the SYSTEM tablespace from the last backup set and then recover the database.
B.
Restore the SYSTEM tablespace image copy using the restore command and then
restore the database.
C.
Use the switch datafile command to instantly switch to the datafile copy, recover the
tablespace, and open the database.
D.
The database is not recoverable in this situation with image copies.
E.
Manually copy the datafile image copy to the correct location and then manually restore
the database from SQL*Plus.
C is correct since restoring from backup set is the slowest method.:
https://docs.oracle.com/cd/B28359_01/backup.111/b28273/rcmsynta049.htm
Example 2-147 Switching to Image Copies to Avoid Restoring from Backup
Assume that a disk fails, rendering all datafiles in the users tablespace inaccessible. Image copies of all datafiles in this tablespace exist in the flash recovery area. After starting RMAN and connecting to the database as TARGET, you can run SWITCH to point to the control file to the new datafiles and then run RECOVER as follows:
SQL “ALTER TABLESPACE users OFFLINE IMMEDIATE”;
SWITCH TABLESPACE users TO COPY;
RECOVER TABLESPACE users;
SQL “ALTER TABLESPACE users ONLINE”;