Being an Oracle DBA in the initial year of our we work on the standalone database. In the world of backup, we work on multiplexing of the redo log. But as in single instance database is different from RAC environment. Multiplexing means to keep multiple copies of redo log in different diskgroup. It is similar to that of multiplexing in standalone, Only change is RAC will have threads for the node.

i.e a 2 node RAC will have 2 threads. So while adding redolog group, we need to mention the thread parameter. Basically, we need to add new redolog groups in required diskgroup and drop the old ones.Now let’s have look on steps which we are going to create multiplexing Redolog in Oracle RAC.

1. Current redo log status:

Currently, the redologs are under +DATA diskgroup, which we will multiplex to +REDOA,+REDOB diskgroup and resize to 5G each.

2. Add logfile groups for node 1 :(THREAD 1)

3. Add logfile groups for node 2 : (THREAD 2)

4. Drop the old redolog groups:

The old redolog groups are 1,2,3,4. And We can drop only the redolog groups whose status is INACTIVE.
Currently group 1, 3 are INACTIVE. Let’s drop them first.

Now we need to drop group 2, 4. But their status is CURRENT. So any attempt to drop these loggroups will result in below error.

ORA-01623: log 1 is current log for instance test (thread 1) – cannot drop


So to make them inactive, switch logfiles multiple time, till the status changes to INACTIVE.

As now both are in the INACTIVE state, Let’s drop them.

Now all the old the redolog groups were dropped. With this multiplexing activity completed.
For resizing redolog groups, we can follow the same above steps.

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