Parallel backup using RMAN in RAC environment

For configuring the number of parallel channel, we can use following command

RMAN> CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COMPRESSED BACKUPSET PARALLELISM 4;

After allocating the channels, if we execute RMAN backup script, we’ll see channel allocation like

allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=104 instance=inst1 devtype=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: sid=66 instance=inst1 devtype=DISK
allocated channel: ORA_DISK_3
channel ORA_DISK_3: sid=94 instance=inst1 devtype=DISK
allocated channel: ORA_DISK_4
channel ORA_DISK_4: sid=40 instance=inst1 devtype=DISK

By default, channels will be allocated from one node. To split the load across all the nodes in the cluster, individual channels need special configuration.

So in two-node cluster, we can equally distribute the load as

CONFIGURE CHANNEL 1 DEVICE TYPE DISK CONNECT ‘sys/passwd@inst1’;
CONFIGURE CHANNEL 2 DEVICE TYPE DISK CONNECT ‘sys/passwd@inst1’;
CONFIGURE CHANNEL 3 DEVICE TYPE DISK CONNECT ‘sys/passwd@inst2’;
CONFIGURE CHANNEL 4 DEVICE TYPE DISK CONNECT ‘sys/passwd@inst2’;

For validating the configuration,

RMAN> show all;

RMAN configuration parameters are:

CONFIGURE CHANNEL 1 DEVICE TYPE DISK CONNECT ‘*’;
CONFIGURE CHANNEL 2 DEVICE TYPE DISK CONNECT ‘*’;
CONFIGURE CHANNEL 3 DEVICE TYPE DISK CONNECT ‘*’;
CONFIGURE CHANNEL 4 DEVICE TYPE DISK CONNECT ‘*’;

Username & passwords will not be shown.

Now if we again, execute same RMAN script, we should see channel allocation like

allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=104 instance=inst1 devtype=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: sid=66 instance=inst1 devtype=DISK

allocated channel: ORA_DISK_3
channel ORA_DISK_3: sid=94 instance=inst2 devtype=DISK
allocated channel: ORA_DISK_4
channel ORA_DISK_4: sid=40 instance=inst2 devtype=DISK

This approach can be used to reduce the backup time.

Caution: Compressed Backup is CPU bound, so number of channels should be carefully used.

If we reduce the degree of parallelism, let’s say from 4 to 2

RMAN> CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COMPRESSED BACKUPSET PARALLELISM 2;

We’ll have 2 redundant channels. In RMAN setting, they will be shown as ignored

configuration for DISK channel 3 is ignored
configuration for DISK channel 4 is ignored

To remove these extra channels, we can use

RMAN> CONFIGURE CHANNEL 3 DEVICE TYPE DISK CLEAR;
RMAN> CONFIGURE CHANNEL 4 DEVICE TYPE DISK CLEAR;