![]() When parallelizing, RMAN always allocates channels in numerical order, beginning with 1 and ending with the parallelism setting. For example, if you configure parallelism to 3, then RMAN allocates three channels of the default device type whenever it uses automatic channels. PARALLELISM command specifies the number of channels that RMAN uses when allocating automatic channels for a specified device type. "Configuring Automatic Channels" to learn how to configure automatic channels If you issue a command such as ALLOCATE or CONFIGURE, then RMAN automatically releases the preallocated channels. For example, RMAN can use the same preallocated channels for the following series of commands: BACKUP DATAFILE 1 RMAN optimizes automatic channel allocation by leaving automatic channels allocated so long as each new command requires exactly the same channel configuration as the previous command. For example, you override automatic channel allocation when you issue a command as follows: RUN You cannot mix automatic and manual channels, so manual channels always override automatic channels. You can override automatic channel allocation settings by manually allocating channels within a RUN block. You use commands within a RUN block but do not allocate any channels within the RUN block.You use commands such as BACKUP, RESTORE, or DELETE outside of a RUN block.RMAN automatically allocates channels according to values set with the CONFIGURE command in the following cases: Unless you manually run an ALLOCATE CHANNEL command, RMAN allocates automatic channels according to the settings in these commands:įor example, you can issue the following commands at the RMAN prompt: BACKUP DATAFILE 3 You can use the manual channel allocation feature you to specify channels for commands used within a RUN block. You can use the automatic channel allocation feature to configure a set of persistent, automatic channels for use in all RMAN sessions. Oracle9i Recovery Manager Reference for ALLOCATE CHANNEL syntax and Oracle9i Recovery Manager Reference on ALLOCATE CHANNEL FOR MAINTENANCE Some media managers allocate resources when you issue the command others do not allocate resources until you open a file for reading or writing. Whether the ALLOCATE CHANNEL command or CONFIGURE CHANNEL causes the media manager to allocate resources is vendor-specific. If you specify channels manually, then the ALLOCATE CHANNEL command (executed only within a RUN command) and ALLOCATE CHANNEL FOR MAINTENANCE command (executed only at the RMAN prompt) specify the type of I/O device that the server session will use to perform the backup, restore, or maintenance operation. For the RESTORE command and the various maintenance commands (for example, DELETE), RMAN determines which device types are required, and allocates all necessary channels. For the BACKUP command, RMAN allocates only a single type of channel, such as DISK or sbt. When you run a command that requires a channel, and you do not allocate a channel manually, then RMAN automatically allocates the channels using the options specified in the CONFIGURE command. In this way, you do not have to allocate channels every time you perform a backup, restore, or recovery operation. You can also run the CONFIGURE CHANNEL command RMAN to specify automatic channels to disk or tape. RMAN comes preconfigured with a DISK channel that you can use for backups and copies to disk. You can either allocate channels manually within a RUN block, or preconfigure channels for use in all RMAN sessions using automatic channel allocation. Text description of the illustration sbr81083.gif Only one RMAN session communicates with the allocated server sessions. The server session performs the backup, restore, and recovery operations. As illustrated in Figure 5-1, each channel establishes a connection from the RMAN executable to a target or auxiliary database instance by starting a server session on the instance. Allocation of one or more RMAN channels is necessary to execute most backup and recovery commands. Oracle9i Real Application Clusters Administration for information about channel allocation and backups in an Oracle Real Application Clusters environmentĪn RMAN channel represents one stream of data to a device type and corresponds to one server session. Hardware Multiplexing by the Media Manager.Channel Control Options for Manual and Automatic Channels.Parallelization for Manually Allocated Channels.Automatic Channel Specific Configurations.Automatic Channel Generic Configurations.Automatic and Manual Channel Allocation.RMAN Automatic and Manual Channel Allocation Control File and Server Parameter File Autobackups.Backup Options: Naming, Sizing, and Speed. ![]() RMAN Automatic and Manual Channel Allocation.This chapter describes the basic concepts involved in using the Recovery Manager (RMAN) utility. RMAN Concepts I: Channels, Backups, and Copies
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