2.4 ALLOCATE CHANNEL
Purpose
ALLOCATE CHANNEL
manually allocates a channel, which is a connection between RMAN and a database instance. The ALLOCATE CHANNEL
command must be issued within a RUN
block. It allocates a channel only in the block where the command is issued.
Prerequisites
The target instance must be started.
Usage Notes
Manually allocated channels are distinct from automatically allocated channels specified with CONFIGURE
. Automatic channels apply to any RMAN job in which you do not manually allocate channels. You can override automatic channel configurations by manually allocating channels within a RUN
command, but you cannot use BACKUP
DEVICE TYPE
or RESTORE
DEVICE TYPE
to use automatic channels after specifying manual channels with ALLOCATE CHANNEL
.
Caution:
If the Oracle Database Windows services is running with a LP user, then you must manually grant the permissions required for the LP user to access the Oracle wallet. Otherwise, RMAN returns the ORA-28759 error message.Multiple Channels
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, with 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 (see Example 2-7). 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 equals the number of tape devices divided by the number of duplexed copies (see Example 2-8).
Channels in an Oracle RAC Environment
If the password for the SYS
and SYSBACKUP
users all Oracle RAC instances is the same, then you do not need to put passwords in the CONNECT
option of the ALLOCATE
or CONFIGURE
command. If you use a connect string of the form user
@
database
, then RMAN automatically uses the same password that was used for the TARGET
connection when the RMAN session was started.
Syntax
allocate::=
Semantics
Syntax Element | Description |
---|---|
|
Specifies a connection between RMAN and an auxiliary database instance. An auxiliary instance is used when executing the See Also: |
|
Specifies a connection between RMAN and the target database instance. The Each connection initiates a database server session on the target or auxiliary instance: this session performs the work of backing up, restoring, or recovering RMAN backups. You cannot make a connection to a shared server session. Whether Each channel operates on one backup set or image copy at a time. RMAN automatically releases the channel at the end of the job. Note: You cannot prefix |
|
Specifies the type of storage for a backup. Query the Note: When you specify See Also: |
Specifies control options for the allocated channel. The channel parameters for sequential I/O devices are platform-specific (see Example 2-6). See Also: |
Examples
Example 2-6 Manually Allocating a Channel for a Backup
This example allocates a single tape channel for a whole database and archived redo log backup. The PARMS
parameter specifies the Oracle Secure Backup media family named wholedb_mf
.
RUN { ALLOCATE CHANNEL c1 DEVICE TYPE sbt PARMS 'ENV=(OB_MEDIA_FAMILY=wholedb_mf)'; BACKUP DATABASE; BACKUP ARCHIVELOG ALL NOT BACKED UP; }
Example 2-7 Distributing a Backup Across Multiple Disks
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 output files are on different disks.
RUN { ALLOCATE CHANNEL disk1 DEVICE TYPE DISK FORMAT '/disk1/%U'; ALLOCATE CHANNEL disk2 DEVICE TYPE DISK FORMAT '/disk2/%U'; BACKUP DATABASE PLUS ARCHIVELOG; }
Example 2-8 Creating Multiple Copies of a Backup on Tape
In this example, four tape drives are available for writing: stape1
, stape2
, stape3
, and stape4
. You use the SET
BACKUP COPIES
command to instruct RMAN to create two identical copies of the database backup. Because the guideline is that the number of tape channels equals the number of tape devices divided by the number of duplexed copies, you allocate two channels. In this case the BACKUP_TAPE_IO_SLAVES
initialization parameter must be set to TRUE
.
In the OB_DEVICE_
n
parameter for Oracle Secure Backup, the n
specifies the copy number of the backup piece. RMAN writes copy 1 of each backup piece to tape drives stape1
and stape2
and writes copy 2 of each backup piece to drives stape3
and stape4
. Thus, each copy of the database backup is distributed between two tape drives, so that part of the data is on each drive.
RUN { ALLOCATE CHANNEL t1 DEVICE TYPE sbt PARMS 'ENV=(OB_DEVICE_1=stape1,OB_DEVICE_2=stape3)'; ALLOCATE CHANNEL t2 DEVICE TYPE sbt PARMS 'ENV=(OB_DEVICE_1=stape2,OB_DEVICE_2=stape4)'; SET BACKUP COPIES 2; BACKUP DATABASE; }
Example 2-9 Allocating an Auxiliary Channel for Database Duplication
This example creates a duplicate database from backups. RMAN can use configured channels for duplication even if they do not specify the AUXILIARY
option. In this example, no SBT channel is preconfigured, so an auxiliary SBT channel is manually allocated.
RUN { ALLOCATE AUXILIARY CHANNEL c1 DEVICE TYPE sbt; DUPLICATE TARGET DATABASE TO dupdb DB_FILE_NAME_CONVERT '/disk2/dbs/','/disk1/' SPFILE PARAMETER_VALUE_CONVERT '/disk2/dbs/', '/disk1/' SET LOG_FILE_NAME_CONVERT '/disk2/dbs/', '/disk1/'; }
See Also:
Oracle Database
Reference for more information on the parameter DB_FILE_NAME_CONVERT