Databases Reference
In-Depth Information
Using rate
You can also use the
rate
clause of the
allocate
channel command or the
configure
channel command to control
RMAN's I/O rate. This example configures channel 1 to have a maximum read rate of 5MB per second:
RMAN> configure channel 1 device type disk rate=5M;
The rate can be set using M, K, or G (for megabytes, kilobytes, and gigabytes). If you need to clear the channel
rate setting, use this command:
RMAN> configure channel 1 device type disk clear;
■
See My Oracle Support note 369573.1 for details on minimizing the impact of an rMan backup on an OLtp
database.
Tip
How It Works
RMAN is engineered to perform backup and recovery tasks as fast as possible. When you initiate a backup, the
backup's execution will increase the I/O on the server as the blocks are read from data files and written to backup
pieces. Sometimes you may want to slow down RMAN so that it doesn't impact application performance while the
backup is running. You can slow down RMAN with the
duration
clause or by specifying a
rate
.
The
duration
clause specifies the amount of time you want an RMAN backup to take. When you use the
minimize load
clause, this instructs RMAN to spread out the I/O load over the duration of the specified time. When
minimizing the load, RMAN will monitor and adjust the I/O rate so that the resources are consumed evenly across
the duration of the backup. The format for the time value of the duration clause is HH:MM (HH is hours and MM is
minutes). You must specify the hour and colon components of the time even if the hour component is zero.
If a backup does not complete within the specified duration period, then RMAN will abort the backup. If you are
running backup commands from within a
run{}
block, then RMAN will not execute subsequent commands. You can
use the
partial
clause to instruct RMAN to continue running subsequent commands within a
run{}
block (even if
the backup doesn't finish in the specified time).
In this example, the
partial
clause instructs RMAN to execute all subsequent commands in the
run{}
block
even if the first command doesn't finish within the specified time:
RMAN> run {
backup duration 1:00 partial minimize load database;
backup archivelog all;
backup current controlfile;
}
Whether or not you use the
partial
clause, RMAN will still consider any backup sets that were created
successfully (before the time limit was exceeded) to be usable for restore operations. If you want to force RMAN to
include only one data file per backup set, you can use the
filesperset
parameter as shown here:
RMAN> backup duration 01:00 minimize load database filesperset 1;
When you set the
filesperset
parameter to 1, it forces RMAN to create each backup set with only one data file
within it. Any backup sets that complete before the duration time is exceeded will be marked as successful.
