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Multiplexing control/redo files

paul.guerin@hp.com asks:

Question

We know that when you multiplex a control file or redolog member to another physical disk, then you effectively have an active backup of the file. The idea being it is unlikely for physical corruption to occur on multiple physical devices at the same time. So if a physical corruption were to occur you still have a multiplexed file on another physical device, that will be unaffected, and you can use this multiplexed file to recover and open the database again. Also after the physical corruption has been resolved you can copy the uncorrupt multiplexed file(s) to a new physical location and establish the multiplexing again. I already have confirmation from Oracle support that multiplexing only protects against physical corruption of the control and redolog files - and not logical corruption of these files. Oracle support also told me they acknowledge that multiplexing is unnecessary where hardware redundancy (eg SAN RAID5) is already being used, however they still recommend multiplexing to give some protection against accidental dropping of control and redolog files. My question - can there be any other justification for multiplexing control and redologs where hardware redundancy (eg SAN RAID5) is already being used?

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