According to Oracle, “Oracle recommends that you multiplex your redo log files. The loss of the log file data can be catastrophic if recovery is required”
Oracle also has a cautionary note on performance that is “When you multiplex the redo log, the database must increase the amount of I/O that it performs. Depending on your configuration, this may impact overall database performance.”
So the question is should we multiplex redo logs with Exadata, which is highly protected from disk failures? The answer YES / NO, It will all depend on your ASM disk group redundancy levels. Oracle recommends making DATA disk group redundancy level high and placing all the online Redo Logs / Standby Logs on DATA disk group and not to be multiplexed.
Please use following Exadata Best practice matrix to decide whether to multiplex online redo logs or not.
- If a high redundancy disk group exists, place all redo logs in that high redundancy disk group.
- If both DATA and RECO are high redundancy, place all redo logs in DATA.
- If only normal redundancy disk groups exist, multiplex redo logs, placing them in separate disk groups.