Databases Reference
In-Depth Information
Log writer
Group 1
Group 2
Group 3
/u01/oraredo/o12c/
redo01a.rdo
/u01/oraredo/o12c/
redo02a.rdo
/u01/oraredo/o12c/
redo03a.rdo
/u02/oraredo/o12c/
redo01b.rdo
/u02/oraredo/o12c/
redo02b.rdo
/u02/oraredo/o12c/
redo03b.rdo
Archiver
Archive Log Sequence 1
Archive Log Sequence 2
Figure 14-1.
Typical online redo log configuration
The online redo log files aren't intended to be backed up. These files contain only the most recent redo
transaction information generated by the database. When you enable archiving, the archived redo log files are the
mechanism for protecting your database transaction history. Therefore, you should back up the archive redo log files.
The contents of the current online redo log files are not archived until a log switch occurs. This means that if you
lose all members of the current online redo log file, then you'll most likely lose transactions. Listed next are several
mechanisms you can implement to minimize the chance of failure with the online redo log files:
•
Multiplex groups to have multiple members.
•
If possible, don't allow two members of the same group to share a controller.
•
If possible, don't put two members of the same group on the same physical disk.
•
Ensure operating system file permissions are set appropriately (restrictive so that only the
owner of the Oracle binaries has permissions to write and read).
•
Use physical storage devices that are redundant (that is, RAID).
•
Appropriately size the log files so that they switch and are archived at regular intervals.
archive_lag_target
initialization parameter to ensure that the online
redo logs are switched at regular intervals.
•
Consider setting the
