Database Reference
In-Depth Information
Here is a corresponding file generated by RMAN:
/u01/O12C/rman/rman_0jnv0557_1_1.bkp
The
%U
instructs RMAN to dynamically construct a unique string for the backup file name. A unique name is
required in most situations, because RMAN won't write over the top of a file that already exists. This is important,
because if you instruct RMAN to write in parallel, it needs to create unique file names for each channel; for example,
RMAN> configure device type disk parallelism 2;
Now, when you run the
BACKUP
command, you see this message:
RMAN> backup database format '/u01/O12C/rman/rman_%U.bkp';
RMAN allocates multiple channels and writes in parallel to two different backup files. The
U%
in the format string
guarantees that unique file names are created.
CONFIGURE CHANNEL...FORMAT
I don't usually use the
BACKUP...FORMAT
syntax to specify the location for RMAN backups. I prefer to use the
CONFIGURE CHANNEL...FORMAT
command. This is because I'm frequently writing to multiple disk locations and need the
flexibility to specify directories located on different mount points. Here is a typical configuration specifying
CONFIGURE CHANNEL...FORMAT
:
RMAN> configure device type disk parallelism 3;
RMAN> configure channel 1 device type disk format '/u01/O12C/rman/rman1_%U.bk';
RMAN> configure channel 2 device type disk format '/u02/O12C/rman/rman2_%U.bk';
RMAN> configure channel 3 device type disk format '/u03/O12C/rman/rman3_%U.bk';
In these lines of code, you should configure the device-type parallelism degree to match the number of channels
that you allocated. RMAN only allocates the number of channels as specified by the degree of parallelism; other
configured channels are ignored. For instance, if you specify a degree of parallelism of 2, RMAN allocates only two
channels, regardless of the number of channels you configured via the
CONFIGURE CHANNEL
command.
In this example of configuring three channels, suppose the
BACKUP
command is issued, like this:
RMAN> backup database;
RMAN allocates three channels, all on separate mount points (
/u01
,
/u02
,
/u03
), and writes in parallel to the
specified locations. RMAN creates as many backup pieces in the three locations as it deems necessary to create a
backup of the database.
If you need to unconfigure a channel, do so as follows:
RMAN> configure channel 3 device type disk clear;
■
also consider what happens if you configure a degree of parallelism higher than the number of preconfigured
channels. rMan will open a channel for each degree of parallelism, and if the number of channels opened is greater than
the number of preconfigured channels, for the unconfigured channels, rMan will write backup files to the fra
(if configured) or the default location.
Note
