Database Reference
In-Depth Information
Backup Sets and Backup Set Pieces
Backup sets are logical entities that consist of one or
more backup set pieces. Backup set pieces are physical files that actually store the RMAN
backup data.
RMAN Channels
Channels
are used in RMAN to indicate the device to back up to. They
are also used to partition a backup operation, essentially parallelizing the operation. For
example, if you had two tape units, you could create two different RMAN channels and
stream your backup to the two different tape devices in parallel. This can reduce backup
and recovery times significantly.
RMAN offers
automated channel failover
for both backup and recovery operations. With
automated channel failover, if a channel in a multichannel backup fails, the other channels will
continue to back up the remainder of the database. This can be helpful when, for example, a
tape device fails. In addition, Oracle will attempt to back up the data that was supposed to be
backed up on the failed channel across the remaining channels.
Snapshot Control File
When RMAN does its business, it bases its knowledge of the data-
base on information in the database control file. That's fine, but if the control file changes
during an RMAN operation, what is RMAN to do—use the old information or the new
information? The answer to this dilemma is the snapshot control file.
When RMAN performs any operation that requires a consistent view of the control file
(such as a backup), it will first create a copy of the control file. This copy is called the
snapshot control file
. The snapshot control file will be used for the duration of that oper-
ation and will be overwritten by any subsequent operation. Even related operations (say,
during a backup database plus archive-log operation that does an archive log backup, a
database backup, and then another archive log backup) will use newly created snapshot
control files, one for each operation.
Getting Started with RMAN
Starting RMAN is very easy to do. It has a simple command line interface (as well as
an interface through Oracle Cloud Control 12
c
). In this chapter we will discuss starting
RMAN, creating and connecting to an account with the SYSBACKUP privilege. Finally
we will look at the command line parameters that you can use with RMAN.
Starting the RMAN Interface
Connecting to the RMAN client is quite simple. RMAN is a command-line tool, so you would
want to open a command-line window for your operating system. Once you have done that
you will set your
ORACLE_HOME
environment to the database that you want to connect to. Now
you can start RMAN and connect to the target database (or the database that you want to
back up and recover). Here is an example of connecting to a database with the RMAN client:
C:\oracle\admin\ORCL\wallet>set oracle_sid=orcl
C:\oracle\admin\ORCL\wallet>rman target=/
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