1. RMAN channel is a connection to a database server session.
  2. RMAN uses channels to perform almost all RMAN tasks.
  3. Use CONFIGURE CHANNEL command to configure options for disk or SBT channels.

Configure RMAN Channel for Disk

RMAN> CONFIGURE CHANNEL DEVICE TYPE DISK MAXPIECESIZE 2G; 

 

Configure RMAN Channel file format

RMAN automatically replaces the format specifier %t with a four byte time stamp, %s with the backup set number, and %p with the backup piece number.

By configuring an explicit format for disk channels, RMAN does not create backups by default in the flash recovery area.

RMAN> CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT /tmp/%U; 
RMAN> CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT '/disk1/ora_df%t_s%s_s%p';

Configure RMAN Channel for SBT Parallelism: Disk and SBT

The number of channels available for a device type when you run a command determines whether RMAN will read or write in parallel. As a rule, the number of channels used in executing a command should match the number of devices accessed. For tape backups, allocate one channel for each tape drive. For disk backups, allocate one channel for each physical disk. Failing to allocate the right number of channels adversely affects RMAN performance during I/O operations.

In the following example RMAN can back up to a media manager using two tape drives in parallel and RMAN allocates one channel for each. Each configured SBT channel will back up roughly half the total data.

RMAN> CONFIGURE DEVICE TYPE sbt PARALLELISM 2;

RMAN Changes the default backup type for the SBT device to an uncompressed backup set.

RMAN> CONFIGURE DEVICE TYPE sbt BACKUP TYPE TO BACKUPSET;

 

In this example RMAN is configued for Disk Parallelism using three channels for each disk drive.

RUN 
{
ALLOCATE CHANNEL disk1 DEVICE TYPE DISK FORMAT '/disk1/%d_backups/%U';
ALLOCATE CHANNEL disk2 DEVICE TYPE DISK FORMAT '/disk2/%d_backups/%U';
ALLOCATE CHANNEL disk3 DEVICE TYPE DISK FORMAT '/disk3/%d_backups/%U';
BACKUP AS COPY DATABASE;
}

 

Configure RMAN Channel for ASM Disk location

You can also specify an ASM disk location.

RMAN> CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT '+dgroup1';

Manually Override Configured RMAN Channel

If you manually allocate a channel during a job, then RMAN disregards any configured channel settings. Must be used within a RUN block as show in follwing example

RUN 
{
ALLOCATE CHANNEL c1 DEVICE TYPE DISK;
BACKUP TABLESPACE users;
}
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