You can set
various channel limit parameters that apply to operations that are performed by
the allocated server session in the CONFIGURE CHANNEL and ALLOCATE CHANNEL
commands.
The
MAXPIECESIZE parameter specifies the maximum size of a backup piece. Use this
parameter to make RMAN create multiple backup pieces in a backup set. RMAN
creates each backup piece with a size that is no larger than the value that has
been specified in the parameter.
The RATE
parameter specifies the bytes per second that RMAN reads on the channel. This
parameter is useful in preventing RMAN from consuming excessive disk bandwidth
and degrading online transaction processing (OLTP) performance. For example, if
each disk drive delivers 3 MB per second and you set RATE=1500K, some disk
bandwidth will still be available to the online system.
The
MAXOPENFILES parameter determines the maximum number of input files that a
backup or copy can have open at a given time. If not set manually, the value
defaults to 8. The level of RMAN multiplexing is partially determined by
MAXOPENFILES. The level of multiplexing in turn determines how RMAN allocates
disk buffers. Multiplexing is the number of input files that are simultaneously
read from and then written into the same backup piece.
If you
configure multiple channels for an SBT device, then you can specifically spread
data files across those channels. Here is an example:
RUN
{
ALLOCATE CHANNEL c1 DEVICE TYPE sbt;
ALLOCATE
CHANNEL c2 DEVICE TYPE sbt;
ALLOCATE
CHANNEL c3 DEVICE TYPE sbt;
BACKUP
(DATAFILE 1,2,5 CHANNEL c1)
(DATAFILE 4,6 CHANNEL
c2)
(DATAFILE 3,7,8
CHANNEL c3);
BACKUP
DATABASE NOT BACKED UP;
}
