ALLOCATE CHANNEL

Syntax

Text description of the illustration rcmsynta33.gif

Purpose

To manually allocate a channel, which is a connection between RMAN and a database instance. Each connection initiates an Oracle server session on the target or auxiliary instance: this server session performs the work of backing up, restoring, or recovering backup sets and copies.

Manually allocated channels (allocated by using ALLOCATE) are mutually exclusive with automatically allocated channels (specified by using CONFIGURE). Manually allocated channels apply only to the RUN job in which you issue the command. Automatic channels apply to any RMAN job in which you do not manually allocate channels. You can always override automatic channel configurations by manually allocating channels within a RUN command.

Each channel operates on one backup set at a time (for BACKUP, RESTORE, or RECOVER) or one image copy at a time (for COPY). RMAN automatically releases the channel at the end of the job.

You can control the degree of parallelism within a job by the number of channels. You can allocate multiple channels simultaneously, thus allowing a single job to read or write multiple backup sets or copies in parallel. If you establish multiple connections, then each connection operates on a separate backup set or file copy.

Whether ALLOCATE CHANNEL causes operating system resources to be allocated depends on the operating system. On some platforms, operating system resources are allocated at the time the command is issued. On other platforms, operating system resources are not allocated until you open a file for reading or writing.

Restrictions and Usage Notes

• Execute ALLOCATE only within the braces of a RUN command.
• The target instance must be started.
• You cannot make a connection to a shared server session.
• You must allocate either a manually allocated or automatic channel when executing a BACKUP, DUPLICATE, COPY, RESTORE, RECOVER, or VALIDATE command.
• You cannot specify BACKUP DEVICE TYPE or RESTORE DEVICE TYPE after running ALLOCATE CHANNEL.
• You must use a recovery catalog when backing up a standby database.
• You cannot prefix ORA_ to a channel name. RMAN reserves channel names beginning with the ORA_ prefix for its own use.

Keywords and Parameters

Syntax Element	Description
AUXILIARY	Specifies a connection between RMAN and an auxiliary database instance. An auxiliary instance is used when executing the DUPLICATE command or performing TSPITR. An auxiliary database can reside on the same host as its parent or on a different host. When specifying this option, the auxiliary database must be mounted but not open. See Also: "DUPLICATE" to learn how to duplicate a database, and "CONNECT" to learn how to connect to a duplicate database
CHANNEL 'channel_id'	Specifies a connection between RMAN and the target database instance. Each connection initiates an Oracle server session on the database instance: this server session performs the work of backing up, restoring, and recovering backups and copies. Specify a channel id, which is the case-sensitive name of the channel, after the CHANNEL keyword. Oracle uses the to report I/O errors.
DEVICE TYPE = deviceSpecifier	Specifies the type of storage device. See Also: "deviceSpecifier" Note: If you do not specify the DEVICE TYPE parameter, then you must specify the NAME parameter to identify a particular sequential I/O device. Query the V$BACKUP_DEVICE view for information about available device types and names.
allocOperandList	Specifies control options for the allocated channel. See Also: "allocOperandList"

Examples

Allocating a Single Channel for a Backup: Example

This command allocates a tape channel for a whole database and archived redo log backup:

RUN
{
  ALLOCATE CHANNEL c1 DEVICE TYPE sbt;
  BACKUP DATABASE PLUS ARCHIVELOG;

}

Spreading a Backup Set Across Multiple Disks: Example

When backing up to disk, you can spread the backup across several disk drives. Allocate one DEVICE TYPE DISK channel for each disk drive and specify the format string so that the filenames are on different disks:

RUN
{
  ALLOCATE CHANNEL disk1 DEVICE TYPE DISK FORMAT '/disk1/backups/%U'; 
  ALLOCATE CHANNEL disk2 DEVICE TYPE DISK FORMAT '/disk2/backups/%U'; 
  BACKUP DATABASE PLUS ARCHIVELOG;
} 

Creating Multiple Copies of a Backup Set: Example

When creating multiple copies of a backup set, you can specify the SET BACKUP COPIES command. The following example generates a single backup of the database, and then creates two identical backups of datafile 1 to two different file systems:

RUN
{
  ALLOCATE CHANNEL c1 DEVICE TYPE DISK MAXPIECESIZE 5M;
  BACKUP DATABASE PLUS ARCHIVELOG;
  SET BACKUP COPIES = 2;
  BACKUP DATAFILE 1 FORMAT '/disk1/backups/%U', '/disk2/backups/%U';
}

Allocating an Auxiliary Channel for Database Duplication: Example

When creating a duplicate database, allocate a channel by using the AUXILIARY option:

RUN
{ 
  ALLOCATE AUXILIARY CHANNEL c1 DEVICE TYPE sbt;
  ALLOCATE AUXILIARY CHANNEL c2 DEVICE TYPE sbt;
  DUPLICATE TARGET DATABASE TO ndbnewh 
    LOGFILE 
      '?/oradata/aux1/redo01.log' SIZE 200K, 
      '?/oradata/aux1/redo02.log' SIZE 200K
      '?/oradata/aux1/redo03.log' SIZE 200K
  SKIP READONLY
  NOFILENAMECHECK;
}