In this post, I will discuss about Oracle Cluster Registry which is a critical component of RAC.
The  Oracle Cluster Registry (OCR)  records cluster configuration information. If it  fails, the entire clustered environment for Oracle 11g RAC will be adversely affected and a possible outage may result if  OCR is lost.
OCR is the central repository for CRS, which stores the metadata, configuration and state information for all cluster resources defined in clusterware. It is a cluster registry used to maintain application resources and their availability within the RAC environment. It also stores configuration information for CRS daemons and clusterwaremanaged applications.
What is stored in OCR ?
  • - Node membership information i.e. which nodes are part of the cluster
  • - Software active version
  • - the location of the 11g voting disk.
  • - Serverpools
  • - Status for the cluster resources such as RAC databases, listeners, instances, and services

  . Server up/down
  . Network up/down
  . Database up/down
  . Instance up/down
  . Listener up/down …

  • - configuration for the cluster resources such as RAC databases, listeners, instances, and services.

  . Dependencies
  . Management policy (automatic/manual)
  . Callout scripts
  . Retries
  . ….- cluster database instance to node mapping

  • - ASM instance, Diskgroups etc.
  • - CRS application resource profiles such as VIP addresses, services etc.
  • - Database services’ characteristics e.g preferred/available nodes, TAF policy , Load balancing goal etc.
  • - Information about clusterware processes
  • - Information about interaction and management of  third party applications controlled by CRS
  • - Details of the network interfaces held by the cluster network
  • - Communication settings where the Clusterware daemons or background processes listen
  • - Information about OCR backups
Let’s take a  peek at the OCR backup …

[root@host01 ~]# ocrconfig -manualbackup
host02     2013/01/18 01:03:40     /u01/app/11.2.0/grid/cdata/cluster01/backup_20130118_010340.ocr
[root@host02 ~]#  strings /u01/app/11.2.0/grid/cdata/cluster01/backup_20130118_010340.ocr| grep -v type |grep ora!
Who updates OCR ?
OCR, which contains information about the high-availability components of the RAC cluster, is maintained and updated by several client applications:
- CSSd during cluster setup  – to update the status of servers
- CSS during node addition/deletion – to add/delete node names
- CRSd about status of nodes during failure/reconfiguration
- SRVCTL (used to manage clusters and RAC databases/instance)
- Cluster control utility – CRSCTL (to manage cluster/local resources)
- Enterprise Manager (EM),
- Database Configuration assistant (DBCA),
- Database Upgrade Assistant (DBUA),
- Network Configuration Assistant (NETCA) and
- the ASM Configuration Assistant (ASMCA).
Each node in the cluster maintains a copy of the OCR in memory for better performance and each node is responsible for updating the OCR as required. The CRSd process is responsible for reading and writing to the OCR files as well as refreshing the local OCR cache and the caches on the other nodes in the cluster.Oracle uses a distributed shared cache architecture during cluster management to optimize queries against the cluster repository. Each node maintains a copy of the OCR in memory. Oracle Clusterware uses a background process to access the OCR cache. Only one CRSd process (designated as the master) in the cluster performs any disk read/write activity. Once any new information is read by the master CRSd process, it performs a refresh of the local OCR cache and the OCR cache on other nodes in the cluster. Since the OCR cache is distributed across all nodes in the cluster, OCR clients (srvctl, crsctl etc.) communicate directly with the local OCR process on the node to obtain required information. Clients communicate via the local CRSd process for any updates on the physical OCR binary file.
 However, the ocrconfig command cannot modify OCR configuration information for nodes that are shut down or for nodes on which Oracle Clusterware is not running. So, you should avoid shutting down nodes while modifying the OCR using the ocrconfig command. If for any reason, any of the nodes in the cluster are shut down while modifying the OCR using the ocrconfig command, you will need to perform a repair on the stopped node before it can brought online to join the cluster.
The ocrconfig –repair command changes the OCR configuration only on the node from which you run this command. For example, if the OCR mirror was relocated to a disk named /dev/raw/raw2 from racnode1 while the node racnode2 was down, then use the command ocrconfig -repair ocrmirror /dev/raw/raw2 on racnode2 while the CRS stack is down on that node to repair its OCR configuration: For a demonstration of ocrconfig -repair, please click here.
Purpose of OCR
- Oracle Clusterware reads the ocr.loc file for the location of the registry and to determine which applications resources need to be started and the nodes on which to start them.
- It is used to bootstrap the CSS for port info, nodes in the cluster and similar info.
- The CRSd, or Oracle Clusterware daemon’s function is to define and manage resources managed by Clusterware. Resources have profiles that define metadata about them. This metadata is stored in the OCR. The CRS reads the OCR and
   . manages the application resources: starts, stops, monitors and manages their failover
   . maintains and tracks information pertaining to the definition, availability, and current state of the services.
   . implements the workload balancing and continuous availability features of services
   . generates events during cluster state changes;
   . maintains configuration profiles of resources in the OCR.
   . records  the currently known state of the cluster on a regular basis and provides the same when queried (using srvctl, crsctl etc.)
How is the info stored in OCR
The OCR uses a file-based repository to store configuration information in a series of key-value pairs, using a directory tree-like structure.It contains information pertaining to all tiers of the clustered database. Various parameters are stored as name-value pairs used and maintained at different levels of the architecture.
Each tier is managed and administrated by daemon processes with appropriate privileges to manage them. For example,
  . all SYSTEM level resource or application definitions would require root, or superuser, privileges to start,
stop, and execute resources defined at this level.
  . those defined at the DATABASE level will require dba privileges to execute.
Where and how should OCR be stored?
  • -  You can find the location of the OCR in a file on each individual node of the cluster. This location varies by platform but on Linux the location of the OCR is stored in the file /etc/oracle/ocr.loc
  • - The OCR must reside on a shared disk(s) that is accessible by all of the nodes in the cluster. In the prior releases of Oracle, the Oracle Cluster Repository (OCR) was on raw devices. Since the raw devices have been deprecated, the choice now is between a cluster filesystem or an ASM diskgroup. The OCR and voting disk  must be on a shared device so a local filesystem is not going to work. Clustered filesystems may not be an option due to high cost. Other options may include network filesystems but they are usually slow and unreliable. So, ASM remains the best choice. The OCR and voting disks could be on any available ASM diskgroup; not ones exclusively created for them.
  • - The OCR is striped and mirrored (if we have a redundancy other than external), similar to ordinary Database Files . So we can now leverage the mirroring capabilities of ASM to mirror the OCR also, without having to use multiple RAW devices for that purpose only.
  • - The OCR is replicated across all the underlying disks of the diskgroup; so failure of a disk does not bring the failure of the diskgroup.
  • - Considering the criticality of the OCR contents to the cluster functionality, Oracle strongly recommends you to multiplex the OCR file. In 11g R2, you can have up to five OCR copies.
  • - Due to its shared location, from a single location, all the components running on all nodes and instances of Oracle can be administrated, irrespective of the node on which the registry was created.
  •  – A small disk of around 300 MB-500 MB is a good choice.

various utilities used to manage OCR
Add an OCR file
Add an OCR file to an ASM diskgroup called +DATA
ocrconfig –add +DATA
Moving the OCR 
Move an existing OCR file to another location :
ocrconfig –replace /u01/app/oracle/ocr –replacement +DATA
Removing an OCR location
- requires that at least one other OCR file must remain online.
ocrconfig –delete +DATA
Migrating to ASM
Oracle Clusterware 11g Release 2 supports the storage of OCR files on ASM. Clusterware makes it easy to migrate your OCR files to ASM. Simply follow these instructions:
1.Check the active version of Clusterware and make sure that it is or greater
#crsctl query crs activeversion
2.Make sure that ASM is running on all nodes.
3.Create a new disk group for the OCR file. It should have a minimum of 1GB of space on it.
4.Use the ocrconfig command to add the OCR file to the new ASM disk group
#ocrconfig –add +NEW_DISKGROUP
5.Remove any OCR storage locations that you no longer wish to use with the ocrconfig command as seen here:
#ocrconfig –delete /u01/shared/OCR1
Migrating Off ASM
If you do not want to store OCR on  ASM you can migrate your OCR files from ASM to other shared storage. Simply follow these instructions:
1.Check the active version of Clusterware and make sure that it is or greater with the crsctl command as seen here:
#crsctl query crs activeversion
2.Create the shared file for the OCR. Make sure that root owns it, that oinstall is the group and with permissions 640. The mount should have at least 300MB of free space.
3.Add any OCR storage locations that you wish with the ocrconfig command as seen here:
#ocrconfig –add /u01/shared/OCR1
4.Use the ocrconfig command to remove the OCR file from ASM disk group
#ocrconfig –delete +OLD_DISKGROUP
OCR repair
If the OCR becomes damaged (which might be evidenced by cluster failures, or error messages in Clusterware logs) then you may need to repair the OCR. Also, if you make a change to the cluster configuration while a node is down then you may need to repair the OCR too. For example if another OCR location was addeed while a node was down, to repair the OCR use the ocrconfig command as seen here:
#ocrconfig –repair –add /u01/app/oracle/ocr
This command will only run on the node  that the command is executed on. Thus, if you stopped a node, made some cluster adjustments on another node and then restarted the down node, you might need to execute the ocrconfig command on the node once it’s started. For a demonstration of ocrconfig -repair, please click here.
OCR Backups
Oracle Clusterware 11g Release 2 backs up the OCR automatically every four hours on a schedule that is dependent on when the node started (not clock time). OCR backups are made to the GRID_HOME/cdata/<cluster name> directory on the node performing the backups. One node known as the master node is dedicated to these backups, but in case master node is down , some other node may become the master. Hence, backups could be spread across nodes due to outages. These backups are named as follows:
-4-hour backups   (3 max) –backup00.ocr, backup01.ocr, and backup02.ocr.
-Daily backups     (2 max) – day.ocr and day_.ocr
-Weekly backups (2 max) – week.ocr and week_.ocr
It is recommended that OCR backups may be placed on a shared location which can be configured using ocrconfig -backuploc <new location> command.
Oracle Clusterware maintains the last three backups, overwriting the older backups. Thus, you will have 3 4-hour backups, the current one, one four hours old and one eight hours old.
Therefore no additional clean-up tasks are required of the DBA. Oracle Clusterware will also take a backup at the end of the day. The last two of these backups are retained. Finally, at the end of each week Oracle will perform another backup, and again the last two of these backups are retained. You should make sure that your routine file system backups backup the OCR location.
Note that RMAN does not backup the OCR.
You can use the ocrconfig command to view the current OCR backups:
#ocrconfig –showbackup auto                                                                                                                                                                                              
If  your cluster is shutdown, then the automatic backups will not occur (nor will the purging). The timer restarts from the beginning when the cluster is restarted. When you start the cluster backup, a backup will not be taken immediately.  Hence, if you are stopping and starting your cluster that you could impact the OCR backups and the backup period could go long beyond 4 hours.
If you feel that you need to backup the OCR immediately (for example, you have made a number of cluster related changes) then you can use the ocrconfig command to perform a manual backup:
#ocrconfig –manualbackup
You can list the manual backups with the ocrconfig command too:
#ocrconfig –showbackup manual
Ocrconfig also supports the creation of a logical backup of the OCR as seen here:
#ocrconfig –export <filename>
It is recommended that the OCR backup location be on a shared file system and that the cluster be configured to write the backups to that file system. To change the location of the OCR backups, you can use the ocrconfig command as seen in this example:
#ocrconfig –backuploc /u01/app/oracle/ocrloc
Note that the ASM Cluster File System (ACFS) does not support storage of OCR backups.
Restoring the OCR
If you back it up, there might come a time to restore it. Recovering the OCR from the physical backups is fairly straight forward, just follow these steps:
1.Locate the OCR backup using the ocrconfig command.
#ocrconfig -showbackup
2.Stop CRS on all nodes one by one
#crsctl stop crs
   If above command fails due to OCR corruption, stop CRS on all nodes one by one using the
  following command:
#crsctl stop crs -f
3.Start CRS on one node in exclusive mode
#crsctl start crs -excl 
   Check if crsd is running. If it is, stop it :
# crsctl stop resource ora.crsd -init
4.Restore the OCR 
If you want to restore OCR to an Oracle ASM disk group, then you must first create a disk group using SQL*Plus that has the same name as the disk group you want to restore and mount it on the local node.
If you cannot mount the disk group locally, then run the following SQL*Plus command:
SQL> drop diskgroup disk_group_name force including contents;
     Restore OCR from its physical backup 
#ocrconfig –restore {path_to_backup/backup_file_to_restore}
5. Verify the integrity of OCR
6. STOP CRS on the node where you had started in exclusive mode
#crsctl stop crs 
If CRS does not stop normally, stop it with force option
#crsctl stop crs -f
7.Start CRS on all nodes one by one
#crsctl start crs
8.Check the integrity of the newly restored OCR:
#cluvfy comp ocr –n all -verbose
I hope you found this information useful. Your comments/suggestions are welcome.
Related links:





  1. Hello
    I have a comment about the restore OCR procedure. In our case, the OCR and Voting Disks are localised in ASM.

    When we made tests restoring the OCR either from the physical backup or the logical backup, the ocrconfig -restore or ocrconfig -import didn’t work !!
    The messages were the following :

    # ocrconfig -restore /HW6_FS_ARCH_SMM/SAUVEOCR/backup_20130109_143035.ocr
    PROT-35: The configured Oracle Cluster Registry locations are not accessible

    # ocrconfig -import /tmp/ocr_export_130109_1434.dmp
    PROT-1: Failed to initialize ocrconfig
    PROC-26: Error while accessing the physical storage
    ORA-29701: unable to connect to Cluster Synchronization Service

    In order to restore the OCR either from an import file or a backup file (automatic or manual), we were obliged to start one CRS node in exclusive and nocrs mode :

    # crsctl start crs -excl -nocrs

    After that, the import or restore commands were OK.

    Then we stop CRS on the first node and we start again all the CRS nodes.
    So it seems that ASM must be started when the OCR is localised on ASM in order to recover an OCR.


      1. Hi Balaji,

        OLR is node specific and contains info about node specific resources only. It is used for startup initially when ASM is not up. After ASM has been started, OCR on ASM becomes accessible and cluster ready services come up.


  2. Hi Anju,

    metadata about OCR backup oracle stores in OCR itself then if my OCR is missing or corrupted the how can I locate backup using ocrconfig -showbackup ?

    1. Hi Balasaheb,

      Since OCR backups are stored in pre-defined location(unless you have configured another location which you are aware of) i.e. GRID_HOME/cdata/, you can locate the backups there.

      Anju Garg

  3. Hello Anju,

    Thanks for reply.

    but still I am confused, how clusterware aware about backup location as my OCR corrupted then in such case from where clusterware take the information about OCR backup ?

  4. Very good explanation and examples. I’m preparing for 1z0-058 and this post helped me get a better understanding of backup/ restore procedures regarding OCR.

Your comments and suggestions are welcome!