6 Replies Latest reply on Apr 12, 2012 2:30 PM by Helios-GunesEROL

    number of control files needed when using ASM

    user12159859
      REF: Oracle 11.2, AIX 7.1 (unix)

      I have a general question regarding the number of controlfiles needed when using ASM, and the placement of them and was hoping I could get some good feedback from the community.

      Oracle has always recommended 3 control files with traditional databases on standard unix file systems.

      Now that we have ASM, what are best practices for number of controlfiles, and placement.

      I've considered only having 1 controlfile in the ASM, but then, I considered perhaps we should have a second controlfile on the operating system too.

      What are your thoughts?
        • 1. Re: number of control files needed when using ASM
          713555
          the reason you have more then is in case you lose 1 or 1 gets corrupted. keep 3 on ASM in different locations if you want.
          • 2. Re: number of control files needed when using ASM
            mseberg
            Hello;

            I would NEVER have just one copy.

            At the very least I would create a copy of each group.

            +dgroup1
            +dgroup2

            Or at the very least put one on the file system and one on ASM

            Documented it here:

            http://www.nixblog.org/post/2010/04/07/Multiplexing-an-Oracle-controlfile-in-ASM


            Best Regards

            mseberg
            1 person found this helpful
            • 3. Re: number of control files needed when using ASM
              user12159859
              By default, Oracle creates a folder in ASM called CONTROLFILE and puts 1 controlfile in this directory.
              This is by default.

              So, I'm wondering why would we need two controlfiles? Is it possible for a controlfile to become corrupt?
              If not, then what is the purpose of having 2 controlfiles in the same location (in ASM).
              If we lose ASM, we lose everything (all databases, all controlfiles, etc.).
              Then, we have to do an RMAN restore of a controlfile and then restore the database and recovery it.

              So, what is the purpose of having multiple controlfiles?

              I can see when we had separate drives and if we lost a drive with a controlfile on it, but this is no longer the case with ASM.
              If we lose a drive (which is just a virtual drive anyway), then we lose the whole ASM and everything in it.

              Edited by: user12159859 on Apr 12, 2012 8:01 AM

              Corrected above: By default, Oracle only puts one controlfile in the ASM (not 2).
              • 4. Re: number of control files needed when using ASM
                user12159859
                I see your point mseberg.

                I didn't want to create a second disk group, but perhaps it would be a best practice.
                At least it makes more sense than keeping two controlfiles in the same folder in ASM (or even in the same disk group).

                As for putting one of the controlfiles on the filesystem (which was my original question), this makes sense to me as well, however, I'm concerned we would get the following type error when we do backups.

                RMAN-06214: Datafile Copy /oraback/rman/lawprod/control02.ctl
                RMAN-08591: WARNING: invalid archived log deletion policy
                • 5. Re: number of control files needed when using ASM
                  713555
                  well, yes they do go corrupt, if you have a second one, stop database, copy good to bad, start database, seconds to do. So now youve got an extra layer of protection and not going looking for rman backups.

                  yes you should have autobackups to disk, rman backups to tape. theyre all part of an overall protection policy.

                  The reason you have them in more then 1 location, eg, dgroup1, dgroup2 is to protect you incase someone was in a deleted all files in a folder by mistake. think it doesnt happen?
                  1 person found this helpful
                  • 6. Re: number of control files needed when using ASM
                    Helios-GunesEROL
                    Hi;

                    Pelase alsos ee:
                    How to duplicate a controlfile when ASM is involved [ID 345180.1]

                    Regard
                    Helios
                    1 person found this helpful