Question about how Oracle manages the Redo logs

Hello

Assuming a configuration which consists of 2 redo log groups (groups A and B), each group of 2 disks (disks A1 and A2 for Group A) and B1 and B2 disks for Group B. Additionally, assume that each redo log file resides by itself in a disk storage device and that the device is dedicated to her. So in the situation described above, there are 4 discs, one for each redo log file, and each disc contains nothing other than a redo log file. Also, assume that the database is in ARCHIVELOG mode and the files from archive is stored on another different set of devices.

kind of graphically:
    GROUP A             GROUP B

      A1                  B1
      A2                  B2
The question is: when the disks that make up the Group A are filled and Oracle switches to the disks in the Group B, can the group drives to take offline, perhaps even physically removed from the system if necessary without affecting the functioning of the database? Can the archiver process temporarily delayed until the disks (which have been removed) are presented online or is the DBA have to wait until the end of the process to archive a copy of the redo log file creating in archive?

Thank you for your help,

John.

Hello
A journal of the groups fall

To remove a group of online redo logs, you must have the ALTER DATABASE system privilege. Before you delete a line redo log group, consider the following precautions and restrictions:

* An instance requires at least two groups of files logging online, regardless of the number of members in the groups. (A group is one or more members.)
* You can delete a group of newspapers online redo only if it is inactive. If you need to drop the current group, first force a log switch occurs.
* Make sure a group of online redo logs is archived (if archiving is enabled) before dropping. To see if this happens, use the view LOG V$.

SELECT GROUP #, ARCHIVED, STATUS FROM V$ LOG;

GROUP # ARC STATUS
--------- --- ----------------
1 ACTIVE YES
2. NO CURRENT
3 INACTIVE YES
4 INACTIVE YES

Delete a group of newspapers online redo with the SQL ALTER DATABASE statement with the DROP LOGFILE clause.

The following statement drops redo log group number 3:

ALTER DATABASE, DROP LOGFILE GROUP 3;

When a group of online redo logs is deleted from the database, and you do not use Oracle managed files, operating system files are not removed from the disk. Instead, control of the associated database files are updated to remove members of the Group of the database structure. After deleting a group of online redo logs, make sure the drop completed successfully and then use the command of operating system appropriate to delete the dropped online redo log files.

When you work with files managed by Oracle, the cleaning of operating system files is done automatically for you.
Your database will not be affected as you can work with 2 files, redo log in each group, as the minimum number of redo log in a database file is two because the process LGWR (newspaper writer) writes in the redo log in a circular way. If the process crashes because you have 2 groups only if you want to remove 1 Add a third and make that the current group and remove the one you want to be offline.

Please refer to:
http://download.Oracle.com/docs/CD/B10500_01/server.920/a96521/onlineredo.htm#7438
Kind regards
Mohamed
Oracle DBA

Tags: Database

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