Specifying the Mode of Log Transmission

The two modes of transmitting archived logs to their destination are normal archiving transmission and standby transmission mode. Normal transmission involves transmitting files to a local disk. Standby transmission involves transmitting files through a network to either a local or remote standby database.

Normal Transmission Mode

In normal transmission mode, the archiving destination is another disk drive of the database server. In this configuration archiving does not contend with other files required by the instance and can complete more quickly. Specify the destination with either the LOG_ARCHIVE_DEST_n or LOG_ARCHIVE_DEST parameters.

It is good practice to move archived redo log files and corresponding database backups from the local disk to permanent inexpensive offline storage media such as tape. A primary value of archived logs is database recovery, so you want to ensure that these logs are safe should disaster strike your primary database.

Standby Transmission Mode

In standby transmission mode, the archiving destination is either a local or remote standby database.

Caution:

You can maintain a standby database on a local disk, but Oracle strongly encourages you to maximize disaster protection by maintaining your standby database at a remote site.

If you are operating your standby database in managed recovery mode, you can keep your standby database synchronized with your source database by automatically applying transmitted archived redo logs.

To transmit files successfully to a standby database, either ARCn or a server process must do the following:

Recognize a remote location
Transmit the archived logs in conjunction with a remote file server (RFS) process that resides on the remote server

Each ARCn process has a corresponding RFS for each standby destination. For example, if three ARCn processes are archiving to two standby databases, then Oracle Database establishes six RFS connections.

You transmit archived logs through a network to a remote location by using Oracle Net Services. Indicate a remote archival by specifying a Oracle Net service name as an attribute of the destination. Oracle Database then translates the service name, through the tnsnames.ora file, to a connect descriptor. The descriptor contains the information necessary for connecting to the remote database. The service name must have an associated database SID, so that the database correctly updates the log history of the control file for the standby database.

The RFS process, which runs on the destination node, acts as a network server to the ARCn client. Essentially, ARCn pushes information to RFS, which transmits it to the standby database.

The RFS process, which is required when archiving to a remote destination, is responsible for the following tasks:

Consuming network I/O from the ARCn process
Creating file names on the standby database by using the STANDBY_ARCHIVE_DEST parameter
Populating the log files at the remote site
Updating the standby database control file (which Recovery Manager can then use for recovery)

Archived redo logs are integral to maintaining a standby database, which is an exact replica of a database. You can operate your database in standby archiving mode, which automatically updates a standby database with archived redo logs from the original database.