RMAN: Setting the Degree of Parallelism with examples

RMAN: Setting the Degree of Parallelism with examples

You can significantly increase the performance of RMAN backup and restore operations if your database server is equipped with the hardware to support multiple channels. If your server has multiple CPUs and multiple storage devices (disks or tape devices), then you can improve performance by enabling multiple backup channels.

If you require better performance from backup and restore operations and have hardware that facilitates parallel operations, you should enable parallelism and perform tests to determine the optimal degree. If your hardware can take advantage of parallel RMAN channels, there is little downside to enabling parallelism.

If you have multiple CPUs, but just one storage device location, you can enable multiple channels to write to and read from one location. For example, if you’re backing up to an FRA, you can still take advantage of multiple channels by enabling parallelism. Suppose you have four CPUs on a server and want to enable a corresponding degree of parallelism:

RMAN> configure device type disk parallelism 4;

You can also write to separate locations in parallel by configuring multiple channels associated with different mount points; for example,

RMAN> configure device type disk parallelism 4;

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';

RMAN> configure channel 4 device type disk format '/u04/O12C/rman/rman4_%U.bk';

This code configures four channels that write to separate locations on disk. When you configure separate channels for different locations, make sure you enable the degree of parallelism to match the number of configured device channels. If you allocate more channels than the specified degree of parallelism, RMAN only writes to the number of channels specified by the degree of parallelism and ignores the other channels.

If you need to clear the degree of parallelism, you can do so as follows:

RMAN> configure device type disk clear;

Similarly, to clear the channel device types, use the CLEAR command. This example clears channel 4:

RMAN> configure channel 4 device type disk clear;

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