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I have three ASM disk groups. OCR, DATA and FRA.

What is the function of OCR? I understand DATA is where all the database files are kept together with the temp files and redo logs and FRA is where archive logs and backups are kept but OCR is what I want to know.

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    – Marcello Miorelli
    Commented Oct 21, 2022 at 9:44
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    OCR is most likely where the cluster registry files and voting files are located.
    – pmdba
    Commented Oct 21, 2022 at 11:54

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The names of disk groups are not pre-determined and have no meaning beyond what the DBA who created them intended. They can be anything, e.g. in my systems we typically have 3 disk groups:

  • DATA - data, control and temp files
  • REDO - online redo log files
  • RECO - recovery area (FRA)

We choose to have a separate REDO disk group so that we can use ultra fast storage for the online redo log files, which has an impact on database performance. The data files can be on less fast storage.

When you install a new ASM system,either Oracle RAC or Restart (stand-alone), the installer will create one disk group where it stores the meta data for the system. Usually this is called DATA, but that is configurable. After the installation completes more disk groups can be added.

As PMDBA already stated, assuming that the names of your disk groups are logically chosen, the OCR disk group would be where the meta data for your cluster is stored. You can check with the asmcmd utility. You would expect at least to see a password file and some ASM entries. This example is from an Oracle Restart system (that has no voting files or OCR):

   $ asmcmd
   ASMCMD> ls *

   +DATA/:
   ASM/
   orapwasm
   ...
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