How many control files on one volume?
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  1. #1
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    How many control files on one volume?

    Hello,

    Another question has rissen in my mind:

    We have a RAID5-SAN. There is only one huge volume where all data remains. Also the control files. When databases are created, Oracle creates 3 control files in the same directory. It doesn't matter where those files are, because when the volume fails, everything fails.

    Question: Because we only have one volume, is it safe to only create two control files?

    I ask this, because performance will decrease when the number of control files increase and vice versa.

    Creating only one, would be best (performance wise), but I think that's a bit tricky!

    A penny for your thoughts...
    An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.

  2. #2
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    If you have only one file system you can not very put them on two or more different file systems.

    However volume failure is not the only threat. You could put them in two or more different directories and that would at least protect them from some potential accidents.

  3. #3
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    Yes, offcourse you are right. Disk corruptions are rare, but it's better to be safe than sorry.

    But... if I have only two control files, stored at separate places and backup the control files regularly to a trace file, than I would have better performance because of the lower number of control files and still have good backups of them. In case of problems, you can restore the control file out of the trace file.

    I had this procedure in mind (from metalink):
    Code:
    CREATE OR REPLACE PROCEDURE proc_control_to_trace AS   
    2   cursor1 INTEGER;   
    3  BEGIN   
    4   cursor1 := dbms_sql.open_cursor;   
    5   dbms_sql.parse(cursor1, 'ALTER DATABASE BACKUP CONTROLFILE TO TRACE',
           dbms_sql.native);   
    6   dbms_sql.close_cursor(cursor1);   
    7  END;
    An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.

  4. #4
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    Originally posted by efrijters
    Yes, offcourse you are right. Disk corruptions are rare, but it's better to be safe than sorry.

    But... if I have only two control files, stored at separate places and backup the control files regularly to a trace file, than I would have better performance because of the lower number of control files and still have good backups of them. In case of problems, you can restore the control file out of the trace file.

    I had this procedure in mind (from metalink):
    Code:
    CREATE OR REPLACE PROCEDURE proc_control_to_trace AS   
    2   cursor1 INTEGER;   
    3  BEGIN   
    4   cursor1 := dbms_sql.open_cursor;   
    5   dbms_sql.parse(cursor1, 'ALTER DATABASE BACKUP CONTROLFILE TO TRACE',
           dbms_sql.native);   
    6   dbms_sql.close_cursor(cursor1);   
    7  END;
    That script just creates a control file creation script, thats all.
    Rather than using ALTER DATABASE BACKUP CONTROLFILE TO TRACE use ALTER DATABASE BACKUP CONTROLFILE TO '/absolutepath/filename.ctl'

    This will copy the actual control file to the specified location.
    Amar
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    Amar's Blog  Get Firefox!

  5. #5
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    Whoops! Okay, my mistake...

    But what do you think of my idea, adewri? Is it sain or not?
    An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.

  6. #6
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    Re: How many control files on one volume?

    Originally posted by efrijters

    Question: Because we only have one volume, is it safe to only create two control files?
    Sure. However, I would put one copy of the control file on another disk even if it is local to the box.



    I ask this, because performance will decrease when the number of control files increase and vice versa. Creating only one, would be best (performance wise), but I think that's a bit tricky!

    Is this a question or a statement? Any performance degradation (very little) is well worth the safety you get by putting another copy of your control file on another physical disk.



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  7. #7
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    I wasn't aware of the amount of overhead when using more/less contol files. Probably it's neglectable...

    Sure. However, I would put one copy of the control file on another disk even if it is local to the box.
    The SAN has no local disks. I can ask the 'network service desk' if it is safe/possible to use a local disk of a server. (The server is in a cluster and maybe this is a problem?)
    An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.

  8. #8
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    Originally posted by efrijters
    The SAN has no local disks. I can ask the 'network service desk' if it is safe/possible to use a local disk of a server. (The server is in a cluster and maybe this is a problem?)
    Mmmm. That's a little more difficult if you're running in a cluster. I would get more disk allocated to you even if it's 10M. The danger you put yourself in with only one volume is a huge obstacle to overcome during a recovery.
    Jeff Hunter
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  9. #9
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    Re: Re: How many control files on one volume?


    Is this a question or a statement? Any performance degradation (very little) is well worth the safety you get by putting another copy of your control file on another physical disk.
    I've never heard of any performance degradation due to control files. The only thing that comes to my mind that would cause any degradation (if any) would be if you're using RMAN and storing RMAN's repository information in the control files. And, the only thing about that is your control files will get bigger.

    Now mirroring Redo logs on a SAN enviornment now that's a different story. let the games begin.
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  10. #10
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    Mirroring redo log files? Well,... uhm.... i hate to say it, but we don't...

    I don't have any info on the SAN (it's a clients system), maybe I can ask them to reconfigure it ("Yes, offcourse! We'll do that right away after you explained to the customers they can't work for a few days...!")

    If they could reconfigure it to multiple volumes (with multiple controllers?), then I could really mirror things... (and probably gain some performance...)


    BTW: I started this thread about control files because the teacher at the Oracle University told me the theory about "multiple control files vs perfromance"...
    Last edited by efrijters; 09-26-2003 at 02:15 PM.
    An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.

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