Configuring RMAN - Pro Oracle Database 12c Administration - page 492

Generally, I instruct RMAN to back up the archive redo logs while the data files are being backed up. This is a
sufficient strategy in most situations. Here is the command to back up the archive redo logs along with the data files:

RMAN> backup database plus archivelog;

Sometimes, if your database generates a great deal of redo, you may need to back up your archive redo logs at a
frequency different from that of the data files. DBAs may back up the archive redo logs two or three times a day; after
the logs are backed up, the DBAs delete them to make room for more current archivelog files.
In most situations, you don't need any archive redo logs that were generated before your last good backup.
For example, if a data file has experienced media failure, you need to restore the data file from a backup and then
apply any archive redo logs that were generated during and after the backup of the data file.
On some occasions, you may need archive redo logs that were generated before the last backup. For instance,
you may experience a media failure, attempt to restore your database from the last good backup, find corruption in
that backup, and therefore need to restore from an older backup. At that point, you need a copy of all archive redo logs
that have been generated since that older backup was made.

Determining the Location for the Snapshot Control File
RMAN requires a read-consistent view of the control file for the following tasks:

• Synchronizing with the recovery catalog

• Backing up the current control file

RMAN creates a snapshot copy of the current control file that it uses as a read-consistent copy while it's
performing these tasks. This ensures that RMAN is working from a copy of the control file that isn't being modified.
The default location of the snapshot control file is OS specific. On Linux platforms the default location/format is
ORACLE_HOME/dbs/snapcf_@.f . Note that the default location isn't in the FRA (even if you've implemented an FRA).
You can display the current snapshot control file details, using the SHOW command:

RMAN> show snapshot controlfile name;

Here is some sample output:

CONFIGURE SNAPSHOT CONTROLFILE NAME TO
'/ora01/app/oracle/product/12.1.0.1/db_1/dbs/snapcf_o12c.f'; # default

For most situations the default location and format of the snapshot control file are sufficient. This file doesn't use
much space or have any intensive I/O requirements. I recommend that you use the default setting.
If you have a good reason to configure the snapshot control file to a nondefault location, you can do so as follows:

RMAN> configure snapshot controlfile name to '/u01/O12C/rman/snapcf.ctl';

If you accidentally configure the snapshot control file location to a nonexistent directory, then when running
a BACKUP or COPY command, the autobackup of the control file will fail, with this error:

ORA-01580: error creating control backup file ...

You can set the snapshot control file back to the default, like this:

RMAN> configure snapshot controlfile name clear;