Allocating a Channel

Question: How is automatic channel allocation used with RMAN to perform backup and restore tasks in Oracle?
In Oracle, Recovery Manager (RMAN) is a robust tool used to perform backup and restore tasks. Automatic channel allocation is a feature of RMAN that allows it to automatically manage resources such as

1. input/output (I/O) operations,
2. parallelism, and
3. load balancing

when performing backup and recovery operations. To use automatic channel allocation, you must configure the RMAN environment to use a media management layer (MML) for backup and restore operations. This is typically done by setting up Oracle Secure Backup (OSB) or a third-party media manager. Here's how automatic channel allocation works with RMAN in the context of backup and restore tasks:

1. Configure channels: Start by configuring the channels in RMAN. Channels represent the I/O resources that RMAN can use during backup and restore operations. By default, RMAN uses a single DISK channel. However, you can configure multiple channels, each with its own settings, to improve performance and parallelism
2. Configure device type: Specify the device type that RMAN will use for backup and restore operations. This can be DISK or SBT (System Backup to Tape) for media manager devices.
3. Set up the media manager: To use automatic channel allocation, you'll need to set up a media management layer (MML) that communicates with RMAN. This can be Oracle Secure Backup (OSB) or a third-party media manager. Make sure to install and configure the MML properly.
4. Set the PARALLELISM parameter: To control the number of channels allocated by RMAN, you can set the PARALLELISM parameter. This setting determines how many channels RMAN will allocate for a specific operation. For example, if PARALLELISM is set to 4, RMAN will automatically allocate up to four channels to perform the backup or restore operation in parallel.
5. Perform backup and restore tasks: Once the channels and media manager are configured, you can use RMAN commands to perform backup and restore tasks. RMAN will automatically allocate and deallocate channels as needed during these operations, improving performance and efficiency.

Here's a simple example of configuring automatic channel allocation:

RMAN> CONFIGURE DEVICE TYPE sbt PARALLELISM 4;
RMAN> CONFIGURE CHANNEL DEVICE TYPE sbt PARMS '<media_manager_specific_parameters>';

Now, when running backup and restore tasks, RMAN will automatically allocate channels based on the configured parallelism and device type settings. Keep in mind that the optimal number of channels and parallelism settings depend on your specific environment, hardware, and workloads. To achieve the best performance, you may need to experiment with different configurations and monitor the impact on backup and restore operations.

You can allocate up to 255 channels; each channel can read up to 64 files in parallel. You can control the degree of parallelism within a job by the number of channels that you allocate. Allocating multiple channels simultaneously allows a single job to read or write multiple backup sets or disk copies in parallel, which each channel operating on a separate backup set or copy. When making backups to disk, the guideline is to allocate one channel for each output device . If RMAN is writing to a striped file system or an ASM disk group, however, then multiple channels can improve performance. When backing up to tape, the guideline is that the number of tape channels should equal the number of tape devices divided by the number of duplexed copies

automatic channel allocation: The ability of RMAN to perform backup and restore tasks without requiring the use of the ALLOCATE CHANNNEL command. You can use the CONFIGURE command to specify disk and tape channels. Then, you can issue commands such as BACKUP and RESTORE at the RMAN command prompt without manually allocating channels. RMAN uses whatever configured channels that it needs to execute the commands.